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Found 11 results

  1. Bash the EM-2 Thread

    Here at Sturgeon's House, we do not shy from the wholesale slaughter of sacred cows. That is, of course, provided that they deserve to be slaughtered. The discipline of Military Science has, perhaps unavoidably, created a number of "paper tigers," weapons that are theoretically attractive, but really fail to work in reality. War is a dangerous sort of activity, so most of the discussion of it must, perforce, remain theoretical. Theory and reality will at some point inevitably diverge, and this creates some heartaches for some people. Terminal, in some cases, such as all those American bomber crews who could never complete a tour of duty over Fortress Europe because the pre-war planners had been completely convinced that the defensive armament of the bombers would be sufficient to see them through. In other cases though, the paper tiger is created post-facto, through the repetition of sloppy research without consulting the primary documents. One of the best examples of a paper tiger is the Tiger tank, a design which you would think was nearly invincible in combat from reading the modern hype of it, but in fact could be fairly easily seen off by 75mm armed Shermans, and occasionally killed by scout vehicles. Add to this chronic, never-solved reliability problems, outrageous production costs, and absurd maintenance demands (ten hours to change a single road wheel?), and you have a tank that really just wasn't very good. And so it is time to set the record straight on another historical design whose legend has outgrown its actual merit, the British EM-2: EM-2ology is a sadly under-developed field of study for gun nerds. There is no authoritative book on the history and design of this rifle. Yes, I am aware of the Collector's Grade book on the subject. I've actually read it and it isn't very good. It isn't very long, and it is quite poorly edited, among other sins devoting several pages to reproducing J.B.S. Haldane's essay On Being the Right Size in full. Why?!!?!! On top of that, there's quite a bit of misinformation that gets repeated as gospel. Hopefully, this thread can serve as a collection point for proper scholarship on this interesting, but bad design. Question One: Why do you say that the EM-2 was bad? Is it because you're an American, and you love trashing everything that comes out of Airstrip One? Why won't America love us? We gave you your language! PLEASE LOVE ME! I AM SO LONELY NOW THAT IT TOLD THE ENTIRE REST OF EUROPE TO FUCK OFF. Answer: I'm saying the EM-2 was a bad design because it was a bad design. Same as British tanks, really. You lot design decent airplanes, but please leave the tanks, rifles and dentistry to the global superpower across the pond that owns you body and soul. Oh, and leave cars to the Japanese. To be honest, Americans can't do those right either. No, I'm not going to launch into some stupid tirade about how all bullpup assault rifle designs are inherently a poor idea. I would agree with the statement that all such designs have so far been poorly executed, but frankly, very few assault rifles that aren't the AR-15 or AK are worth a damn, so that's hardly surprising. In fact, the length savings that a bullpup design provides are very attractive provided that the designer takes the ergonomic challenges into consideration (and this the EM-2 designers did, with some unique solutions). Actually, there were two problems with the EM-2, and neither had anything to do with being a bullpup. The first problem is that it didn't fucking work, and the second problem is that there was absolutely no way the EM-2 could have been mass-produced without completely re-thinking the design. See this test record for exhaustive documentation of the fact that the EM-2 did not work. Points of note: -In less than ten thousand rounds the headspace of two of the EM-2s increased by .009 and .012 inches. That is an order of magnitude larger than what is usually considered safe tolerances for headspace. -The EM-2 was less reliable than an M1 Garand. Note that, contrary to popular assertion, the EM-2 was not particularly reliable in dust. It was just less unreliable in dust than the other two designs, and that all three were less reliable than an M1 Garand. -The EM-2 was shockingly inaccurate with the ammunition provided and shot 14 MOA at 100 yards. Seriously, look it up, that's what the test says. There are clapped-out AKs buried for years in the Laotian jungle that shoot better than that. -The EM-2 had more parts breakages than any other rifle tested. -The EM-2 had more parts than any other rifle tested. -The fact that the EM-2 had a high bolt carrier velocity and problems with light primer strikes in full auto suggests it was suffering from bolt carrier bounce. As for the gun being completely un-suited to mass production, watch this video: Question Two: But the EM-2 could have been developed into a good weapon system if the meanie-head Yanks hadn't insisted on the 7.62x51mm cartridge, which was too large and powerful for the EM-2 to handle! Anyone who repeats this one is ignorant of how bolt thrust works, and has done zero research on the EM-2. In other words, anyone who says this is stupid and should feel bad for being stupid. The maximum force exerted on the bolt of a firearm is the peak pressure multiplied by the interior area of the cartridge case. You know, like you'd expect given the dimensional identities of force, area and pressure, if you were the sort of person who could do basic dimensional analysis, i.e. not a stupid one. Later version of the British 7mm cartridge had the same case head diameter as the 7.62x51mm NATO, so converting the design to fire the larger ammunition was not only possible but was actually done. In fact, most the EM-2s made were in 7.62x51mm. It was even possible to chamber the EM-2 in .30-06. I'm not going to say that this was because the basic action was strong enough to handle the 7x43mm, and therefore also strong enough to handle the 7.62x51mm NATO, because the headspace problems encountered in the 1950 test show that it really wasn't up to snuff with the weaker ammunition. But I think it's fair to say that the EM-2 was roughly equally as capable of bashing itself to pieces in 7mm, 7.62 NATO or .30-06 flavor. Question Three: You're being mean and intentionally provocative. Didn't you say that there were some good things about the design? I did imply that there were some good aspects of the design, but I was lying. Actually, there's only one good idea in the entire design. But it's a really good idea, and I'm actually surprised that nobody has copied it. If you look at the patent, you can see that the magazine catch is extremely complicated. However, per the US Army test report the magazine and magazine catch design were robust and reliable. What makes the EM-2 special is how the bolt behaves during a reload. Like many rifles, the EM-2 has a tab on the magazine follower that pushes up the bolt catch in the receiver. This locks the bolt open after the last shot, which helps to inform the soldier that the rifle is empty. This part is nothing special; AR-15s, SKSs, FALs and many other rifles do this. What is special is what happens when a fresh magazine is inserted. There is an additional lever in each magazine that is pushed by the magazine follower when the follower is in the top position of the magazine. This lever will trip the bolt catch of the rifle provided that the follower is not in the top position; i.e. if the magazine has any ammunition in it. This means that the reload drill for an EM-2 is to fire the rifle until it is empty and the bolt locks back, then pull out the empty magazine, and put in a fresh one. That's it; no fussing with the charging handle, no hitting a bolt release. When the first magazine runs empty the bolt gets locked open, and as soon as a loaded one is inserted the bolt closes itself again. This is a very good solution to the problem of fast reloads in a bullpup (or any other firearm). It's so clever that I'm actually surprised that nobody has copied it. Question Four: But what about the intermediate cartridge the EM-2 fired? Doesn't that represent a lost opportunity vis a vis the too powerful 7.62 NATO? Sort of, but not really. The 7mm ammunition the EM-2 fired went through several iterations, becoming increasingly powerful. The earliest versions of the 7mm ammunition had similar ballistics to Soviet 7.62x39mm, while the last versions were only a hair less powerful than 7.62x51mm NATO. As for the 7mm ammunition having some optimum balance between weight, recoil and trajectory, I'm skeptical. The bullets the 7mm cartridges used were not particularly aerodynamic, so while they enjoyed good sectional density and (in the earlier stages) moderate recoil, it's not like they were getting everything they could have out of the design. note the flat base In addition, the .280 ammunition was miserably inaccurate. Check the US rifle tests; the .280 chambered proto-FAL couldn't hit anything either.
  2. Top Speed in Tanks

    Tank design is often conceptualized as a balance between mobility, protection and firepower. This is, at best, a messy and imprecise conceptualization. It is messy because these three traits cannot be completely separated from each other. An APC, for example, that provides basic protection against small arms fire and shell fragments is effectively more mobile than an open-topped vehicle because the APC can traverse areas swept by artillery fires that are closed off entirely to the open-topped vehicle. It is an imprecise conceptualization because broad ideas like "mobility" are very complex in practice. The M1 Abrams burns more fuel than the Leo 2, but the Leo 2 requires diesel fuel, while the omnivorous AGT-1500 will run happily on anything liquid and flammable. Which has better strategic mobility? Soviet rail gauge was slightly wider than Western European standard; 3.32 vs 3.15 meters. But Soviet tanks in the Cold War were generally kept lighter and smaller, and had to be in order to be moved in large numbers on a rail and road network that was not as robust as that further west. So if NATO and the Warsaw Pact had switched tanks in the late 1950s, they would both have downgraded the strategic mobility of their forces, as the Soviet tanks would be slightly too wide for unrestricted movement on rails in the free world, and the NATO tanks would have demanded more logistical support per tank than evil atheist commie formations were designed to provide. So instead of wading into a deep and subtle subject, I am going to write about something that is extremely simple and easy to describe in mathematical terms; the top speed of a tank moving in a straight line. Because it is so simple and straightforward to understand, it is also nearly meaningless in terms of the combat performance of a tank. In short, the top speed of a tank is limited by three things; the gear ratio limit, the power limit and the suspension limit. The tank's maximum speed will be whichever of these limits is the lowest on a given terrain. The top speed of a tank is of limited significance, even from a tactical perspective, because the tank's ability to exploit its top speed is constrained by other factors. A high top speed, however, looks great on sales brochures, and there are examples of tanks that were designed with pointlessly high top speeds in order to overawe people who needed impressing. When this baby hits 88 miles per hour, you're going to see some serious shit. The Gear Ratio Limit Every engine has a maximum speed at which it can turn. Often, the engine is artificially governed to a maximum speed slightly less than what it is mechanically capable of in order to reduce wear. Additionally, most piston engines develop their maximum power at slightly less than their maximum speed due to valve timing issues: A typical power/speed relationship for an Otto Cycle engine. Otto Cycle engines are primitive devices that are only used when the Brayton Cycle Master Race is unavailable. Most tanks have predominantly or purely mechanical drivetrains, which exchange rotational speed for torque by easily measurable ratios. The maximum rotational speed of the engine, multiplied by the gear ratio of the highest gear in the transmission multiplied by the gear ratio of the final drives multiplied by the circumference of the drive sprocket will equal the gear ratio limit of the tank. The tank is unable to achieve higher speeds than the gear ratio limit because it physically cannot spin its tracks around any faster. Most spec sheets don't actually give out the transmission ratios in different gears, but such excessively detailed specification sheets are provided in Germany's Tiger Tanks by Hilary Doyle and Thomas Jentz. The gear ratios, final drive ratios, and maximum engine RPM of the Tiger II are all provided, along with a handy table of the vehicle's maximum speed in each gear. In eighth gear, the top speed is given as 41.5 KPH, but that is at an engine speed of 3000 RPM, and in reality the German tank engines were governed to less than that in order to conserve their service life. At a more realistic 2500 RPM, the mighty Tiger II would have managed 34.6 KPH. In principle there are analogous limits for electrical and hydraulic drive components based on free speeds and stall torques, but they are a little more complicated to actually calculate. Part of the transmission from an M4 Sherman, picture from Jeeps_Guns_Tanks' great Sherman website The Power Limit So a Tiger II could totally go 34.6 KPH in combat, right? Well, perhaps. And by "perhaps," I mean "lolololololol, fuck no." I defy you to find me a test report where anybody manages to get a Tiger II over 33 KPH. While the meticulous engineers of Henschel did accurately transcribe the gear ratios of the transmission and final drive accurately, and did manage to use their tape measures correctly when measuring the drive sprockets, their rosy projections of the top speed did not account for the power limit. As a tank moves, power from the engine is wasted in various ways and so is unavailable to accelerate the tank. As the tank goes faster and faster, the magnitude of these power-wasting phenomena grows, until there is no surplus power to accelerate the tank any more. The system reaches equilibrium, and the tank maxes out at some top speed where it hits its power limit (unless, of course, the tank hits its gear ratio limit first). The actual power available to a tank is not the same as the gross power of the motor. Some of the gross horsepower of the motor has to be directed to fans to cool the engine (except, of course, in the case of the Brayton Cycle Master Race, whose engines are almost completely self-cooling). The transmission and final drives are not perfectly efficient either, and waste a significant amount of the power flowing through them as heat. As a result of this, the actual power available at the sprocket is typically between 61% and 74% of the engine's quoted gross power. Once the power does hit the drive sprocket, it is wasted in overcoming the friction of the tank's tracks, in churning up the ground the tank is on, and in aerodynamic drag. I have helpfully listed these in the order of decreasing importance. The drag coefficient of a cube (which is a sufficiently accurate physical representation of a Tiger II) is .8. This, multiplied by half the fluid density of air (1.2 kg/m^3) times the velocity (9.4 m/s) squared times a rough frontal area of 3.8 by 3 meters gives a force of 483 newtons of drag. This multiplied by the velocity of the tiger II gives 4.5 kilowatts, or about six horsepower lost to drag. With the governor installed, the HL 230 could put out about 580 horsepower, which would be four hundred something horses at the sprocket, so the aerodynamic drag would be 1.5% of the total available power. Negligible. Tanks are just too slow to lose much power to aerodynamic effects. Losses to the soil can be important, depending on the surface the tank is operating on. On a nice, hard surface like a paved road there will be minimal losses between the tank's tracks and the surface. Off-road, however, the tank's tracks will start to sink into soil or mud, and more power will be wasted in churning up the soil. If the soil is loose or boggy enough, the tank will simply sink in and be immobilized. Tanks that spread their weight out over a larger area will lose less power, and be able to traverse soft soils at higher speed. This paper from the UK shows the relationship between mean maximum pressure (MMP), and the increase in rolling resistance on various soils and sands in excruciating detail. In general, tanks with more track area, with more and bigger road wheels, and with longer track pitch will have lower MMP, and will sink into soft soils less and therefore lose less top speed. The largest loss of power usually comes from friction within the tracks themselves. This is sometimes called rolling resistance, but this term is also used to mean other, subtly different things, so it pays to be precise. Compared to wheeled vehicles, tracked vehicles have extremely high rolling resistance, and lose a lot of power just keeping the tracks turning. Rolling resistance is generally expressed as a dimensionless coefficient, CR, which multiplied against vehicle weight gives the force of friction. This chart from R.M. Ogorkiewicz' Technology of Tanks shows experimentally determined rolling resistance coefficients for various tracked vehicles: The rolling resistance coefficients given here show that a tracked vehicle going on ideal testing ground conditions is about as efficient as a car driving over loose gravel. It also shows that the rolling resistance increases with vehicle speed. A rough approximation of this increase in CR is given by the equation CR=A+BV, where A and B are constants and V is vehicle speed. Ogorkiewicz explains: It should be noted that the lubricated needle bearing track joints of which he speaks were only ever used by the Germans in WWII because they were insanely complicated. Band tracks have lower rolling resistance than metal link tracks, but they really aren't practical for vehicles much above thirty tonnes. Other ways of reducing rolling resistance include using larger road wheels, omitting return rollers, and reducing track tension. Obviously, there are practical limits to these approaches. To calculate power losses due to rolling resistance, multiply vehicle weight by CR by vehicle velocity to get power lost. The velocity at which the power lost to rolling resistance equals the power available at the sprocket is the power limit on the speed of the tank. The Suspension Limit The suspension limit on speed is starting to get dangerously far away from the world of spherical, frictionless horses where everything is easy to calculate using simple algebra, so I will be brief. In addition to the continents of the world not being completely comprised of paved surfaces that minimize rolling resistance, the continents of the world are also not perfectly flat. This means that in order to travel at high speed off road, tanks require some sort of suspension or else they would shake their crews into jelly. If the crew is being shaken too much to operate effectively, then it doesn't really matter if a tank has a high enough gear ratio limit or power limit to go faster. This is also particularly obnoxious because suspension performance is difficult to quantify, as it involves resonance frequencies, damping coefficients, and a bunch of other complicated shit. Suffice it to say, then, that a very rough estimate of the ride-smoothing qualities of a tank's suspension can be made from the total travel of its road wheels: This chart from Technology of Tanks is helpful. A more detailed discussion of the subject of tank suspension can be found here. The Real World Rudely Intrudes So, how useful is high top speed in a tank in messy, hard-to-mathematically-express reality? The answer might surprise you! A Wehrmacht M.A.N. combustotron Ausf G We'll take some whacks at everyone's favorite whipping boy; the Panther. A US report on a captured Panther Ausf G gives its top speed on roads as an absolutely blistering 60 KPH on roads. The Soviets could only get their captured Ausf D to do 50 KPH, but compared to a Sherman, which is generally only credited with 40 KPH on roads, that's alarmingly fast. So, would this mean that the Panther enjoyed a mobility advantage over the Sherman? Would this mean that it was better able to make quick advances and daring flanking maneuvers during a battle? No. In field tests the British found the panther to have lower off-road speed than a Churchill VII (the panther had a slightly busted transmission though). In the same American report that credits the Panther Ausf G with a 60 KPH top speed on roads, it was found that off road the panther was almost exactly as fast as an M4A376W, with individual Shermans slightly outpacing the big cat or lagging behind it slightly. Another US report from January 1945 states that over courses with many turns and curves, the Sherman would pull out ahead because the Sherman lost less speed negotiating corners. Clearly, the Panther's advantage in straight line speed did not translate into better mobility in any combat scenario that did not involve drag racing. So what was going on with the Panther? How could it leave everything but light tanks in the dust on a straight highway, but be outpaced by the ponderous Churchill heavy tank in actual field tests? Panther Ausf A tanks captured by the Soviets A British report from 1946 on the Panther's transmission explains what's going on. The Panther's transmission had seven forward gears, but off-road it really couldn't make it out of fifth. In other words, the Panther had an extremely high gear ratio limit that allowed it exceptional speed on roads. However, the Panther's mediocre power to weight ratio (nominally 13 hp/ton for the RPM limited HL 230) meant that once the tank was off road and fighting mud, it only had a mediocre power limit. Indeed, it is a testament to the efficiency of the Panther's running gear that it could keep up with Shermans at all, since the Panther's power to weight ratio was about 20% lower than that particular variant of Sherman. There were other factors limiting the Panther's speed in practical circumstances. The geared steering system used in the Panther had different steering radii based on what gear the Panther was in. The higher the gear, the wider the turn. In theory this was excellent, but in practice the designers chose too wide a turn radius for each gear, which meant that for any but the gentlest turns the Panther's drive would need to slow down and downshift in order to complete the turn, thus sacrificing any speed advantage his tank enjoyed. So why would a tank be designed in such a strange fashion? The British thought that the Panther was originally designed to be much lighter, and that the transmission had never been re-designed in order to compensate. Given the weight gain that the Panther experienced early in development, this explanation seems like it may be partially true. However, when interrogated, Ernst Kniepkamp, a senior engineer in Germany's wartime tank development bureaucracy, stated that the additional gears were there simply to give the Panther a high speed on roads, because it looked good to senior generals. So, this is the danger in evaluating tanks based on extremely simplistic performance metrics that look good on paper. They may be simple to digest and simple to calculate, but in the messy real world, they may mean simply nothing.
  3. I'm sure that all the SH regulars will know this backwards and forwards, so this is more for the benefit of newer people, or people who stumble in via google, or people who want a quick link they can throw out as an answer to anyone who asks the question. So, what's with the goofy-ass road wheel design on German WWII AFVs? A puzzled and terrified worker struggles to comprehend and assemble the suspension of a tiger I You may have run into a variety of explanations for this running gear design; that it provided a smoother ride, that the design saved rubber, or possibly some other rubbish. Like the myth that frontal drive sprockets provide more traction (seriously, how in the hell is that supposed to make any sense?), these wrong explanations of the merits of interleaved road wheels seem to rise from some quote taken out of context. The interleaved road wheel running gear may have saved some rubber relative to an alternative design that was particularly wasteful of it. But interleaved road wheels are not particularly economic in this respect because, and I realize this is a complicated concept to explain so I'll try my best, they have more wheels. Interleaved road wheels do allow for large wheel diameters, and a larger diameter wheel will spread wear out over a larger circumference. So interleaved road wheels might allow for the rubber on the wheels to last longer, although their construction would require more in the first place. Interleaved road wheels would not improve ride quality either. The ride quality of a tank is not a function of the size or number of wheels it possesses, but of how they are sprung. So, it is possible that in certain competitive trials an interleaved road wheel design outperformed a design that lacked this feature. I could readily believe, for instance, that the tiger (H) had a better ride quality on rough terrain than the tiger (P), or that the SDKFZ. 251 had a smoother ride than the M3. However, this would be because the tiger (H) and SDKFZ. 251 have independently sprung road wheels on torsion bars while the tiger (P) and M3 do not. Torsion bar layout of the tiger II Volute spring suspension of the M3 half track So, what do interleaved road wheels do? They have two principal effects; one is a small benefit, and the other is an enormous detriment. The small benefit of interleaved road wheels is that they spread the weight of the vehicle out more evenly on the track links: The weight of a tank is not completely evenly spread out on the contact area of its tracks. This is because tracks are not rigid. If they were, they would be mainly ornamental and tanks' engines would just be for show. More of the weight of a tank is concentrated under the parts of the track that the road wheels are sitting directly on top of. Additionally, once a tank starts to sink into the soil a bit, larger road wheels work better than smaller ones because the larger ones have more contact area. But you can only fit so many large diameter road wheels in the space of a tank's hull. Dynamic! So, the only way to have lots of road wheels and have big road wheels at the same time is to interleave them. Simple as that. If you would like an exhaustive look at the development of the semi-empirical MMP equation, read this. The major, crippling downside to interleaved road wheels is that it makes changing the road wheels extremely time consuming. A pair of workers perform maintenance on a panther tank, and contemplate the futility of all human achievement Lucas Friedli reprints in his book on big cat maintenance a report from a training unit complaining that replacing the inner road wheels of a tiger tank took ten hours. That is completely outrageous, and was a contributor to the poor operational availability of the big cats. For this reason, interleaved road wheels have rarely been used after World War Two; only on a few French prototypes and a Swedish APC: PBV 302 variant with interleaved road wheels Some bizarre French tank
  4. 56K unfriendliness follows: Artistic 3D cutaway of the GSh-18 from Abiator In the early 1990s, the Russian military began looking for a replacement for the long-serving Makarov PM pistol. The Makarov, while a sound and simple design, was an old-fashioned design that could not take advantage of the latest advances in polymer and ammunition technology. A certain Austrian businessman had shown that it was quite possible to make pistol frames out of injection-molded plastic instead of laboriously milling them out of steel or aluminum, and the world had well and truly taken note. In addition, powerful new armor-piercing ammunition had been developed in Russia that was too much for the simple action of the Makarov pistol to handle. The 7N31 9x19mm round. The bullet consists of a steel penetrator wrapped in a lightweight jacket. The propellant burns at extremely high pressure for a 9x19 round and will wreck Glocks. The two leading contenders were the GSh-18 and the PYA. Both designs used locked breech operation with very beefy locking geometry in both designs to handle the large bolt thrust of the new armor-piercing ammo. Additionally, both designs featured two-column magazines to give them much greater capacity than old PM (17 rounds for the PYA and 18 for the GSh-18). However, while the PYA used a hammer and a traditional metal frame, the GSh-18 was quite in line with the latest thinking in small arms design and used striker firing and a polymer frame. The PYA pistol In any event, the economic and political chaos of the 1990s permitted only limited replacement of the Makarov within the Russian military. The 1950's vintage PM is still a common sight with Russian soldiers. A Russian soldier with a slung AK-74M reloads his Makarov pistol The GSh-18, from Forgotten Weapons The GSh-18's unusual aesthetics and excellent lineage earned it plenty of attention from weapons nerds in the West. Anyone familiar with Soviet aircraft armament knows the names Grayazev-Shipunov. Could this pistol be a diamond in the rough? A future champion, waiting to explode onto the world market? A Russian Glock? Well, thanks to a set of pictures that LoooSeR posted from photographer and MVD operator KARDEN, we now know that the answer is NO. The quality of construction of these pistols... leaves something to be desired. In fairness, some of the roughness is because this particular specimen has been hit with a file to de-fang it; apparently slide bite is a problem with this design. Still; the huge gaps between parts, the very rust-colored finish... it's something that a tribesman with a hammer in the Khyber pass might take pride in, but it's damn rough for a mass-produced product. Karden has commented on several other eyebrow-raising flaws of the design. An unacknowledged champion it is not. But the GSh-18 does have some novel features that are worthy of note and investigation. Take note, aspiring pistol designers who want to design a Glock-killer (I'm pretty sure S&W execs sit in front of a giant poster of Gaston Glock, chanting "To the last, I grapple with thee; From Hell's heart, I stab at thee; For hate's sake, I spit my last breath at thee." over and over again). This design has some spiffy features that deserve copying. How spiffy? Let's start with the fact that the slide isn't a single machined piece. It's two stamping and a machined lockup insert permanently attached to each other with a removable breech block: Again, try to ignore the rough quality of the actual construction, and look at the contours of the parts. The radial ring of locking splines inside the slide is separated from the rest of the slide by a slight step. Furthermore, going from the rear portion of the slide to inside the locking ring this inside diameter gets larger, while going from the muzzle end back this diameter gets smaller. Looking inside the return spring tunnel, we see an acute inside angle between the locking ring and the return spring tunnel. All of these features show that the forward part of the slide is comprised of three parts that are permanently attached together. The locking ring is one piece that is most likely broached before being attached to the main portion of the slide and then to the return spring tunnel front piece. This picture shows that the breech face of the slide is a separate part that comes off for disassembly. There are several small advantages of this arrangement. Instead of laboriously machining the slide from a single piece of bar stock, the breech face can be made separately and inserted into a comparatively simple slide that is "U" shaped in cross section. Laboriously making the slide from a single piece of bar stock, from Brian Nelson's tour of the STI factory In fact, the KBP Instrument Design Bureau has gone one better on simplifying the construction of the slide. Look at it carefully: The sides and top of the slide are of a consistent thickness everywhere. That's right; the GSh-18 has a stamped slide! Albeit, it's one of the thickest stampings I've ever seen in a personal firearm. This is rather similar to early SIG P220 series handguns: A comparison of an early, stamped SIG P226 above and a later milled model, from TTAG Considering that the stamped SIG P226 was changed to a milled slide to prevent the slide and breech block from separating when firing very hot ammo, it is impressive that the GSh-18 uses this sort of construction given that it is designed for a steady diet of the extremely energetic 7N31. For high-volume this sort of slide construction would be much cheaper and faster than the all-milled construction seen in the widely-copied Austrian pistol (The Glock With a Thousand Young). The difference might not be large, but as I've said before, anything in a pistol design that's even slightly cleverer than a Glock deserves attention. Additionally, the two-piece construction of the slide would make caliber conversions easier. A caliber conversion kit would only need to consist of a new barrel, breech block and magazines for the new caliber. The GSh-18 is a rotating barrel pistol design. This itself is nothing new; the patent on that system of operation dates to 1897, but the implementation is unusual. In a typical rotating barrel pistol, the locking occurs at the rear of the barrel, near or in the ejection port and is effected by a few large lugs. The Beretta PX4 is typical: Beretta PX4 from the Genitron review In the GSh-18, however, the locking occurs near the front of the barrel, on the rearward of the two sets of radial barrel projections. The forward projections are not locking lugs; they are beveled on the front and lack witness marks from locking. Furthermore, the locking ring has only one set of splines. The purpose of the forward pseudo-lugs is not clear to me, but they are probably for some prosaic purpose like keeping shit from getting in from the front of the gun. There are a few advantages to this arrangement versus the traditional rear location for locking lugs in a rotating barrel pistol. In a typical rotating barrel pistol with the locking lugs near the firing chamber, there must be a large amount of dead space inside the slide to accommodate the locking lugs when the slide recoil to extract and eject. This gives most rotating barrel pistols fairly chunky slides: CZ 07 with tilting barrel on the left, Grand Power P1 mk 7 with a rotating barrel on the right. From the Walther forums. The GSh-18's locking lug arrangement neatly sidesteps this problem, although the designers ignored this fact. GSh-18 has a very wide slide with a lot of free space inside: GSh-18 and PYA compared So the designers of GSh-18 discovered a solution to one of the drawbacks of rotating barrel locking, even though they did not take advantage of it! Because the slide is stamped, and stampings (especially of that thickness) are somewhat limited in how many fine details and contours they can have, the interaction between the slide and the frame works differently in the GSh-18. Like other short-recoil automatic pistols, the barrel and slide of the GSh-18 are locked together at the moment of firing. Recoil flings the barrel and slide rearward, which causes the lug on the bottom of the barrel to ride over a helical cam cut into a machined piece of steel located in the frame (this piece also acts as a locator for the return spring, and a mount for a spring-loaded claw whose purpose will be discussed shortly): The barrel then stops against this piece while the slide continues recoiling. This causes the slide to extract the spent case and eject it. The slide runs out of velocity as it compresses the recoil spring. Once it has completely compressed the spring, the slide begins moving forward, which causes it to pick up a new round from the magazine. Up to this point, the operation of the GSh-18 is like any other recoil-operated pistol. The difference is with the feeding of the new round into the firing chamber of the barrel. In most other designs there is some interference geometry between the slide and barrel that prevents the barrel from creeping forward from the force of the round being fed into it. If the barrel were allowed to creep forward, it would slide back over the helical cam cut and move into the locked position. This would cause the locking ring splines to bounce off of the locking lugs when the slide came forward, and the gun would not go into battery. But the GSh-18 cannot be made with this sort of detailed interference geometry because the slide is stamped, and making this approach impractical. Instead, there is a large, claw-like lever on the right side of the frame. When the barrel and slide initially retreat during recoil, this claw snaps over a rim on the right side of the barrel. This claw forcibly holds the barrel to the rear until the slide levers it open at the right moment for locking to begin. This locking claw allows the use of a simple stamped slide, but it has some advantages beside that. In a normal pistol, the interference geometry between the slide and barrel causes some amount of friction. This means that the area where the slide rubs against the barrel is a critical lubrication point: Lubrication points for a Glock pistol, from the USA Carry lubrication gude So the GSh-18's slide loses a little less energy from this rubbing, and is also made a little less sensitive to the condition of the lubrication around the barrel. This is probably as good a place as any to mention that certain features of the GSh-18 bear more than a passing resemblance to the ill-starred Colt All-American 2000: The multiple, radially symmetrical locking lugs of the barrel (relocated on the GSh-18 to the front, of course), the two-piece construction of the slide and broad similarities make me wonder if the All-American 2000 was a starting point for the design of the GSh-18. If so, it would make the GSh-18 the second time that this design family with visionary qualities was let down by sub-standard manufacturing. Perhaps the third time is a charm.
  5. The Aglockalypse

    It is time to explain The Aglockalypse. This is the handgun that killed handgun design in the West. Nobody has had any new ideas worth mentioning on the mechanical design of service handguns since this design came out. Almost every major arms manufacturer in the West makes what is materially a Glock clone; albeit with a few small embellishments and their own logo stamped on the side. What Makes a Glock a Glock? Almost every mechanical contrivance in small arms design was invented about one hundred years ago by some Austro-Hungarian noble you've never heard of or by John Moses Browning. It's about 50/50. Most of small arms design these days consists of applying new materials and manufacturing techniques to old ideas (which may have been unworkable at the time), or by taking a lot of old ideas from different sources and mixing them together in some way that's complimentary. The Glock pistol design is no exception; the ideas were not novel, but putting them all together proved an absolutely world-beating combination. 1) Polymer Frame An H&K VP-70, the first production polymer-framed pistol. Polymer-framed pistols were not an original idea, but at the debut of the Glock 17 they were still a fairly new idea. Glock proved the concept to be mature, and it provided the Glock with a huge advantage over the competition. Traditional metal-framed pistols are made by taking a hunk of metal, either a casting, billet or forging, and cutting away everything that isn't pistol-shaped: This translates to a lot of machine time and a lot of expensive alloys that end up as shavings on the floor. The frame of the Glock was much faster and cheaper to make. Some metal inserts were put into an injection mold (which admittedly is an expensive device, but you pay for it once), and then hot, liquid plastic was squirted into this cavity to form the frame. The entire process takes less than a minute. Cost-wise there is no way for a metal-framed pistol to compete with a polymer-framed one, apples to apples. For very large contracts the math tilts even further in favor of injection molding, since one-time capital costs are a large percentage of injection molding costs while ongoing costs are smaller, while ongoing costs for machining stay largely the same. Gaston Glock was very aggressive about pursuing large contracts (notably the NYPD, which was an early coup), which helped him best use this advantage. 2) The Glock locking system Glocks use a linkless Browning tilting-barrel short recoil system and lock the slide to the barrel via a large rectangular lug machined into the barrel that fits into the ejection port. Glocks were the second major pistol design to combine these two concepts, the first being the SiG P220 series. Ejection port of a Webley automatic pistol, showing the square breech section of the barrel locked to the slide via the ejection port. The barrel translates diagonally. Cross section of a Browning hi-power. This was the first mass-produced pistol to use the linkless short recoil system. The barrel locks to the slide via a series of rings in the barrel that tilt into corresponding grooves in the slide. SiG P220 This operating system is robust and reliable, and fairly easy to manufacture. It has a few theoretical flaws, such as the barrel being slightly off-angle during the extraction of the spent case, the pivot sitting below the barrel and thereby raising the bore axis, and the necessary clearances for the movement of the barrel degrading accuracy. In practice these objections are immaterial. Glocks are absurdly reliable, have a low enough bore axis and only a unusually skilled shooters would notice the mechanical contributions of the precision of the pistol over their own wobbling aim. 3) The Glock Fire Control System The Glock fire control group is an elegant combination of several ideas. Again, most of the ideas in the Glock fire control group had antecedents, but their combination and execution in the Glock was very clever. The trigger transfer bar is a complex shape, but it is stamped from sheet metal and so quite cheap to produce. It also combines several functions into a single piece, including enough safeties that Glocks are reasonably safe to carry even though they lack an external safety. The complete lack of a machined metal hammer, and the clever trigger dingus-lever were also cost savings over traditional pistol design. There are several other incidental design features of the Glock pistol, but these three are in my opinion the ones that allowed it to gobble up market share because they economized manufacture. They are also the three features that the overwhelming majority of Western pistols designed since the Early '80s copy unashamedly. Victims of the Aglockalypse When Gaston Glock first entered his creation in the Austrian Army pistol competition, nobody in arms design had heard of the guy. Longstanding Austrian arms company Steyr was quite confident that their own GB pistol would win the competition. This is basically the pistol equivalent of the couple making out in the back of a convertible at night in a horror movie. It is remembered only as the first in a long list of casualties. Instead, not only was the Steyr GB to lose the competition, but it would fade from the marketplace without making much of an impression anywhere. This is a shame, in my opinion, because the Steyr GB has a few good ideas that deserve a second look, such as the two-position-feed magazines (seen otherwise only in rifles, SMGs and Russian pistol designs), and the truckbed-liner crinkle finish. The design also has some good features for economy of production and excellent mechanical precision, but really, on the whole, it's completely inferior to the Glock. These pistols have a really poor reputation for being unreliable and wearing out quickly, and while Steyr fans will claim this is in large part due to inferior license-produced versions from the United States, nobody argues that even the Steyr-made GBs have anything on the nearly bomb-proof Glock. Also, they're enormous. As far as the Glock was concerned, the Steyr GB was just the first blood. It wasn't enough to best a local competitor; the Glock would obsolete an entire generation of automatic pistol designs. In neighboring Germany, Heckler and Koch's flagship pistol offering was the P7. The P7 has many admirable features. Like the Steyr GB it has a fixed barrel and excellent mechanical precision. It is also very slim and has an extremely low bore axis. It also has the most hideously complicated fire control system ever seen in a pistol that isn't a revolver: A pistol like the P7 could simply never be made cost-competitive with the Glock, much less by a company like HK which usually errs on the side of high performance rather than low cost. Walther, the other big German small arms manufacturer, was busy making the P5: No, the picture isn't reversed. The ejection port is indeed on the left side of the P5, which is because the P5 is nothing more than a slightly re-worked P38 of World War Two vintage. The frame is aluminum, the barrel is shorter and the fire control group has some detail improvements, but it's otherwise the same, right down to the dubious rotating-block locking system. It didn't even have a double-column magazine. Just another outdated design for the Glock to drop-kick into the dustbin of history. Longtime Belgian designer FNH was pushing the Browning BDA, a pistol so boring that I can barely write about it while remaining awake. This is basically a Browning hi-power with a double action trigger somehow shoehorned in. Given how the Browning hi-power trigger works, this is not exactly a straightforward conversion, and this would invite curiousity were it not for the fact that this pistol carries with it a highly stiffling aura of impenetrable boringness. I seriously cannot bring myself to care. Across the Atlantic, in gun-happy America the Glock would face stiff competition from hardened, skillful American firms that had more to offer than face-lifted wartime designs and botique gas-delayed guns. The rugged American outlook on law enforcement provided a stiffly competitive market for quality peace officers' weapons. Haha, I kid. They were just as complacent and mediocre as everyone else. Sturm Ruger Co, one of only two publicly traded firearms manufacturers in the US, released their P-series of pistols in the mid eighties. It seems a little uncharitable to list these chunky pistols as victims of Glock superiority, since they sold in decent numbers and aren't terrible. But victims they were; the design was simply outdated. The strangest feature of the P-series pistols is that the older designs in the family use a swinging link to cam the barrel in and out of engagement with the slide. While the swinging cam arrangement works well enough, and several fine weapons use it (e.g. 1911, Tokarev), with modern materials and manufacturing tolerances the linkless system is simply better because it doesn't produce the grinding movement caused by the short radius of the link swinging radius, and because it has fewer parts. The P series was also reasonably cost-competitive because most of the parts are cast before machining to final dimensions. Sturm Ruger has exceptional expertise in firearms castings, which has long given them the edge in pricing. Castings can be made very closely to the final shapes required, which saves a lot of machining time. However, this gives many of their designs a bloated, water-retaining look. The other publicly traded firm, Smith and Wesson, was doing reasonably well with a whole family of automatic pistols that I absolutely do not care about. They have names that end in "9", have generally Browning-ish insides, and the single stacks look pretty and elegant. There are also some double stack variants, and some are in stainless. Something something unbuttoned pastel shirts, designer Italian pants and cocaine. Oh look, there goes my mind, wandering again because these pistols are BORING, MEDIOCRE AND I HAVE MORE IMPORTANT THINGS TO CARE ABOUT. OH LOOK IT'S ANOTHER PRE-GLOCK SINGLE STACK METAL FRAMED PISTOL. This time it's from Colt. It is a well-documented fact that Colt's senior management spent the entire 1980's doing nothing but licking their own genitals like cats. I don't even know what this pistol is called. Do you know what it's called? Do you care? Do you think Colt's management cared? Of course not. So let's make up a name. We'll call it... the Colt Elantra. This Colt pistol is more interesting, and has an operatic history. Unfortunately, that opera is Wagner's Ring Cycle. Nobody did anything that made sense, and by the end there was a fat lady singing and then everything burned to the ground. The pistol was originally designed by Reed Knight and Eugene Stoner, who were by that time already living legends for designing the combat robots that crushed the communist menace decisively at the Battle of Arrakis. The design was mechanically fascinating, featuring an unusual rotating barrel, roller-bearing supported striker fire control group, polymer frame with screw-on grips, and an unusual, but very appealing slide stop design. Alas, Colt completely screwed up the design by making it too big, making the trigger pull too long and too heavy, and by making it not work. Even without the stiff competition from Glock, the design would have been an ignominious failure. All of the above designs, though in some cases initially successful, would face dwindling market share against the cheaper-to produce Glocks. Their respective firms sat down and quickly came to the conclusion that they were not as clever as Gaston Glock, but that was OK since he had done the clever for them. Saint Gaston Converts the Industry to Glocktholicism The first of the Glock clones to hit the market, the S&W Sigma is so similar to the Glock that some of the parts will interchange: This resulted in some drama, hasty design changes and a settlement payment for an undisclosed amount. Next came the Walther P99: This pistol introduced the interchangeable backstrap, which was generally considered a good idea. It also introduced several option trigger modules, including a DA/SA version with a decocker button on top of the slide. This is bid'ah, and heresy against the Glockspel. The great genius of the Glock is that it's simpler and cheaper to produce than competing designs. One cannot successfully outcompete the Glock by taking a Glock and adding a bunch of extra shit to it. Then you just have a more expensive Glock, which, ipso facto, will not outcompete an Orthodox Glock. HK was, until recently, one of the last holdouts of Albigensianism hammer-fired handguns, being unable for some time to bring themselves to make an unabashed Glock clone. However, their USP series is, compared to their previous offerings, quite Glocky. They have switched to the Browning short-recoil, linkless tilting barrel design with a barrel that locks to the slide through the ejection port. By 2014, however, HK had entered into full Glockmmunion, and introduced the VP9; a striker-fired, polymer framed pistol: FNH of Belgium initially responded with the FN Forty-Nine, which is like a Glock but with a DAO trigger: However, they swiftly recanted of their error and introduced the FNP, FNX and finally the FNS, an all-but-Orthodox Glock clone: Steyr introduced the M9 series of pistols, which were actually designed by a former Glock employee! These are basically Glocks, but slanted, with weird sights and that say "Steyr" on the side instead of "Glock." In 2007, Ruger was converted and introduced the SR-9: In 2005, S&W made a slightly more refined clone called the M&P: There are several versions now, including some for blasphemers that have external safeties. Colt has yet to introduce a Glock clone; their strategy regarding this portion of the handgun market remains enigmatic. Survivors For various reasons, a few metal-framed designs have survived and remain commercially competitive. But there is reason to think that their days are numbered. The Beretta M92 series is mechanically rather similar to the Walther P-39, except it has a double stack magazine. The widespread adoption of this essentially sound, but uninspired design, by many militaries not the least of which is the US Army, has bought the design staying power. However, the recent announcement that Beretta, too, has discovered how to stencil their own name on to the side of a Glock shows that they haven't come up with anything better either. The CZ-75 design continues on as well, in no small part because producing a CZ-75 clone is a right of passage in Turkey that all adolescents must pass in order to be recognized as men. Turkish CZ-75 clones are so common at firearms trade shows that they are often used for paperweights and juggling. When there is heavy snow it is common to keep a bucket of Turkish CZ-75 clones handy to pour onto icy patches to get better traction for a stuck vehicle. But the latest offering from CZ proper, the CZ P-09 is beginning to look a lot like Glock-mas: Polymer frame, barrel that locks into the ejection port... It keeps the distinctive CZ-75 slide-inside-frame and fire control group, but it's more like a Glock than a CZ-75 is. The trendline is unmistakable. There are a few other hold-outs, but by and large the firearms industry has found Glock's recipe to be compelling. To be cost-competitive, new designs copy these innovations to a greater, rather than a lesser degree. This has meant a stultifying lack of creativity amongst pistol manufacturers, as more and more of them decide that their best bet is to copy a thirty five year old design.
  6. Most automatic weapons, with the exception of really weird designs like the Madsen LMG and Hino-Komuro, have a linear reciprocating breech member; either the bolt or a bolt carrier group. This reciprocating member is supposed to move rearward (the recoil stroke) and pull the spent case from the chamber, and then rebound off of a spring to shove a new round into the chamber (the counter-recoil stroke). After the counter-recoil stroke the reciprocating mass should come to a halt in its forward-most position; the "in-battery" position. When the bolt carrier group is in battery the case is entirely surrounded by the walls of the firing chamber and the locking mechanism is fully engaged, so it is safe to fire. Things do not always work ideally, however, and sometimes this reciprocating mass bounces instead of coming to rest. This is called (somewhat erroneously in the case of gas-operated weapons) "bolt-bounce." Andrew Tuohy removed the buffer weights from the buffer in an AR-15 to make the action bouncier for illustrative purposes: There are two ways that bolt carrier rebound can be a problem. In extreme cases the bolt carrier will rebound, but a combination of high friction in the action and weak return springs will mean that the bolt carrier gets stuck and does not go back into battery. Hopefully the designer was smart enough to design the thing so that it absolutely cannot fire when it is out of battery, because out of battery cartridge ignition is an excellent way to convert a firearm into a pipe bomb. If they were so wise, then there will be a failure to fire of some variety. Generally speaking a weapon has to be unusually dirty, worn, or poorly designed for this problem to occur. Return springs are usually strong enough to get the moving parts into battery even if they aren't fully compressed. I have, however, witnessed this problem in German K43 rifles because they are a pile of suck and fail. But they're pretty. The second, more likely problem only rears its ugly head in fully auto fire. In most full auto weapons there is an auto-sear, which a secondary sear which releases the hammer as long as the trigger is depressed. The auto-sear is tripped by the bolt carrier during counter-recoil, usually when or just before the bolt carrier goes into battery. If the bolt carrier rebounds off the front of the receiver and the timing is just wrong, the hammer (or striker) will hit the bolt carrier when it is slightly out of battery. Again, competent designs have means of preventing out of battery ignition and the attendant facial and manual reorganization that tends to go with that. However, when the hammer or striker hits the out of battery bolt carrier its kinetic energy will be spent. This means a failure to fire. Early M16s had rebound problems, particularly during full auto fire. Originally the buffer was intended simply to be a hollow spring guide, but a problem with light primer strikes forced a redesign of this component in 1966. This image, from the patent for the improved buffer shows the series of sliding weights that were added to the buffer. These work like the sliding pellets in a deadblow hammer and arrest the tendency for the bolt carrier to bounce. The additional mass had the added benefit of slowing down the velocity of the bolt carrier, which reduced wear on the parts and lowered the cyclic rate of fire, which improved full auto control. The HK roller-retarded blowback guns, owing to their extremely high bolt carrier velocities, have a strong tendency to rebound unless somehow checked. The solution HK engineers hit on is an anti-rebound claw: Labeled as the "bolt head locking lever" in this diagram. This is a spring-loaded claw mounted on the bolt carrier that grabs the bolt head as the bolt carrier group goes into battery. The lever essentially ratchets into place with friction, providing enough resistance to being re-opened that the bolt carrier does not rebound. The FAMAS, which has a similarly insanely high bolt carrier velocity, solves the problem in a very similar way. In this case, however, the charging handle is the anti-rebound device. The arrangement is similar to the locking catch on an AR-15's charging handle, except that it's much more robust because the catch is responsible for arresting the rebound of the entire bolt carrier. There are other ways still to arrest the rebound of the bolt carrier. The Ruger MP-9 (the one designed by Uziel Gal, not the insanely over complex B&T product of the same name) is supposed to have a spring-cushioning pad at the front of the receiver which brings the bolt to a stop instead of bouncing. The upcoming Desert Tech MDR has, by one account, "an asymmetrical [bolt carrier] face. This is accomplished with a protruding boss on one side of the carrier. As the carrier moves forward to go into battery, the asymmetrical face contacts the barrel extension first. Tolerances within the axial motion of the back end of the carrier group permit the energy to be redirected through a sideways movement. This micro-movement of the rear end of the carrier impedes the bounce and assures full function of the weapon, especially in select-fire operation." Large caliber autocannons often have complex, articulated secondary locks that prevent bolt carrier bounce, since autocannon bolt carriers are enormous and have a great deal of residual kinetic energy. So, when I read that the SIG MCX has some problems with full auto function that sound suspiciously exactly like the same problems the M16 had prior to the addition of the weighted buffer (the same weighted buffer the MCX does away with), I can only roll my eyes. This is nothing new, and there are a half-dozen ways of fixing it. Do your homework.
  7. The Museum of Retrotechnology

    Too often technology is portrayed a steady, linear series of more or less inevitable improvements. This is an easier illusion to maintain if you don't know anything about the subject. In fact, the history of technology is littered with insane, unworkable garbage. Things that didn't work, barely worked, might-have-beens, things that would perhaps be worth revisiting, things fit only for ridicule, and some things that make no sense whatsoever: Yes! Terrify your enemies with your new gunspoon! Note the direction of the trigger and the direction of the muzzle. What the hell were these even for? Attaching solid fuel rockets to a bicycle! We totes verified this idea in Kerbal Space Program, it'll be fine. An external combustion motor that uses ether instead of steam! Nothing could possibly go wrong with this! A turbine powered by boiling mercury! There is definitely nothing at all that could go horribly wrong with this! Douglas Self's Museum of Retrotechnology Site has all of these wondrous devices and more. Feast your mind on the retardation of the engineers and inventors of yesteryear, and be amazed that anyone is left alive on this planet. "Steampunk" ain't got shit.
  8. Now that Weaponsman has linked the forum, I guess it's time to post actual content. No more dumb one-liners or jokes about the Turkish government's policy towards Kurds or Sherman burning down Atlanta. For at least five posts. I think that's all I can manage. The internet has been a mixed blessing for gun nuts. On the one hand, it allowed for much freer exchange of information that was previously exclusive to a few experts. The notorious mil-spec chart (no longer up to date) that circulated around ar15.com years ago is probably a big part of the reason that AR-15 manufacturers stepped up their game and started turning out generally excellent products. On the other hand, the internet has been an excellent vector for the spread of nonsense. In my experience, relatively little of the misinformation is maliciously spread; it's mostly the result of people not knowing what the hell they are talking about. In particular, a great deal of nonsense would be ignored if people could just remember high school physics. A lot of mystical, physics-defying rubbish is said about weapons reliability in particular. Reading nothing but internet fora circa the late 2000s, one could easily come away with the impression that the AR-15 is uniquely unreliable thanks to the direct impingement action. This is despite the fact that coating aluminum or steel in a thin layer of carbon powder would actually reduce its coefficient of friction. Actually, the dynamics of automatic weapons are not difficult to understand. An often overlooked metric in the reliability of gas-operated automatic weapons is the mass ratio between the bolt and the bolt carrier. I first became aware of the importance of this ratio when reading a US Army manual on small arms design at Forgotten Weapons. Just to be clear, this ratio is only important in the way I'm describing in gas-operated, some recoil-operated and inertia-operated weapons. The dynamics for retarded blowback weapons, like the H&K G3, are quite different. In a gas-operated weapon, there is a bolt that is locked rigidly either to the barrel or to the receiver at the moment of firing. This contains the pressure of the cartridge firing (which is alarmingly high). The projectile is pushed down the bore. As soon as it passes the gas port, some of the gas begins pushing the bolt carrier to the rear. The work done on the bolt carrier by the propellant gas from the gas port is the only energy that the bolt carrier will have to complete the cycle of operations. This means that the total work required to: unlock the bolt pick up the bolt extract the spent case cock the hammer compress the return spring operate the belt mechanism (if it's belt fed) cannot exceed the amount of energy that is initially fed to the bolt carrier. Ideally, the bolt carrier will have some excess reserve of energy so that it can complete the cycle of operations even if the gas port is slightly clogged, the ammunition is slightly under-loaded, or the receiver is dirty (et cetera). However, if the bolt carrier has too great a reserve of kinetic energy, it will still be travelling rapidly when it reaches the end of its travel, and then it will violently jerk to a halt or possibly even bounce off of the rear of the receiver. This increases wear on the weapon, and in a shoulder fired weapon can cause the sights to jerk off target. There are two ways to increase the energy capacity of the bolt carrier; make it go faster (in gas-operated weapons, this is done by the simple expedient of enlarging the gas port), or make it heavier. There are practical limits on how fast the bolt carrier can reciprocate; according to Brassey's, a good rule of thumb is 15 m/s is the maximum practical velocity of the bolt carrier. Above this velocity things start to break. Cases can be torn apart instead of cleanly extracted from the firing chamber (the Soviet SHKAS fast-firing aircraft machine gun required special high-quality ammunition with extra-strong cartridge cases), springs lose their strength in fewer cycles, and the lifespan of the moving parts is reduced due to increased fatigue. Making the bolt carrier heavier also has practical limitations; the weapon becomes heavier not just from the heavier bolt carrier, but also from the larger receiver needed to enclose it. In shoulder-fired weapons the sights will be thrown off target by the porpoising motion of the reciprocating center of mass. The act of picking up the bolt after it is unlocked is of particular interest, because it can absorb a great deal of the energy from the bolt carrier. The bolt is picked up and accelerated by the bolt carrier, after which they are stationary relative to each other. This means that there is an inelastic collision between the bolt carrier and the bolt, and in an inelastic collision kinetic energy is not conserved even though momentum is. The initial kinetic energy of the carrier is 1/2MV^2. The initial and final momentum of the system will be the velocity of all moving mass times that mass. This works out to a reduction in kinetic energy after the pickup of the bolt. For instance, if the bolt and bolt carrier have equal mass, after bolt pickup the velocity of the bolt carrier group will be half of what it was before and the mass double what it was before. That works out to half the kinetic energy of the bolt before pickup. Generally the equation for the remaining energy after bolt pickup will be: E2=E1*(1+1/R)-1 Where E2 is the bolt carrier group kinetic energy after bolt pickup, E1 is the bolt carrier kinetic energy before pickup, and R is the ratio of mass between the bolt carrier and the bolt. If anyone is terribly curious I can show the derivation of this. According to the US Army Ordnance small arms design manual hosted at Forgotten Weapons, designers should shoot for a mass ratio of 3 or better, which would translate to 75% energy retention after bolt pickup. More is better, but there are strong diminishing returns here; a weapon with a mass ratio of 2 will have 66% remaining kinetic energy after bolt pickup, but a design with a mass ratio of 4 will have 80% conservation. As the mass ratio gets larger and larger, the percentage of bolt carrier kinetic energy after bolt pickup will approach 100% asymptotically. Again, to keep designs lightweight, the ideal way to achieve this would be to make the bolt as light as possible. However, in a locked breech weapon in 5.56 NATO, the bolt has to withstand peak chamber forces of 22.7 KN (or 5,100 lbs if you're using haram infidel non-SI units). It therefore has to be fairly robustly constructed, and making a lightweight bolt that is still safe over the operating life of the weapon is not an easy engineering task. When determining the ratio for actual weapons, it's important to define exactly what masses are involved. What we are looking at is the ratio of the moving mass that is accelerated by gas that will have kinetic energy available to accelerate the stationary mass. Take a look at this slow-motion video of an FAL firing: The piston follows the bolt carrier back far enough that its energy is available for bolt pickup, even though it's a separate piece from the carrier and doesn't translate through the entire distance that the bolt carrier does during cycling. So, for the purposes of determining bolt carrier to bolt mass ratio, the piston of the FAL counts as bolt carrier mass. In an AR-15, the firing pin rides in the bolt carrier, is pressed forward against the bolt carrier during the initial acceleration, and therefore counts towards the mass of the bolt carrier group. However, the buffer is not rigidly attached to the bolt carrier, so its kinetic energy cannot contribute towards bolt pickup. Therefore it does not get counted. Obviously any extractors, cam pins, and miscellaneous other parts get counted toward the part they ride with. Strictly speaking some portion of the mass of the return spring should be counted (and Chinn's excellent The Machine Gun has equations for calculating the impact of spring mass on reciprocating parts dynamics), but I was too lazy to include this because it's really, really small. So, let's see how well actual designs do: Semi-auto TAR-21 carrier group mass: .623 kg bolt mass: .055 kg Carrier to bolt mass ratio: ~10:1 Notes: It is impossible to remove the return spring from the bolt carrier of the semi-auto TAR-21 for some arcane reason, so I had to guesstimate on this one. However, whatever the exact number, the TAR-21 has an exceptionally high bolt carrier to bolt mass ratio, and that is one of the (few) outstanding features of the design. Using a stationary cam pin that is located in the bolt carrier that acts upon stationary cam grooves in the bolt is one way that the design improves the mass ratio, and this unusual feature is worth emulating in other designs. Sadly, the design as a whole is not as elegant and mass-efficient as the bolt carrier group is. SIG-551A1 carrier group mass: .505 kg bolt mass: .093 kg Carrier to bolt mass ratio: 4.4 Notes: Disappointingly low, but still above the magic 3:1 figure. The SIG rifles show one of the advantages of a reciprocating charging handle; the mass of the charging handle is adding to the kinetic energy of the bolt carrier, rather than being deadweight. The bolt on the SIG rifles is fairly massive, in part because the firing pin is located in the bolt rather than the bolt carrier. 7.62x39mm AK carrier group mass: .505 kg Bolt mass: .080 kg Carrier to bolt mass ratio: 5.3 Notes: The charging handle and piston are one piece with the bolt carrier on an AK, which helps improve the mass ratio. The bolt is fairly massive, in part because the firing pin is located in the bolt. Semi-Auto SCAR-H carrier group mass: .713 kg Bolt mass .066 kg carrier to bolt mass ratio: 9.8 Notes: In the AR-18 derived bolt carrier designs the cam pin is rigidly attached to the bolt, and therefore increases its mass. Also, the bolt must be sturdy enough to withstand the stress of 7.62 NATO ammunition. Despite this, the SCAR-H manages a monstrous 9.8 mass ratio in a rifle that's still reasonably light for an automatic 7.62 NATO weapon.
  9. Some years ago I was goofing around with a tavor: And a somewhat... less practical design as well: Upon field stripping them, I noticed something interesting: The desert eagle's bolt is on the left, and the tavor's is on the right. They're surprisingly similar. The cam surface for the bolt rotation is located on the bolt stem. In most other rotating bolt designs the cam surfaces are located on the bolt carrier, not the bolt. This is the TAR-21 bolt carrier: You can see the hole where the cam pin sits (it's the big one you can see the wood grain through). In most designs, like the AR-15, the cam pin is attached to the bolt and translates past the bolt carrier. In the tavor it's the other way around. Some older designs like the Lewis and its many progeny also work like this, but ever since the M1 garand the fashion has been to place the lug on the bolt and the cam on the carrier. As you can see, the desert eagle works exactly the same way: The cam pin is removed, and you can see the slot it sits in as well as the bolt cam surfaces just showing through. The similarities do not end there: In the above image you can see the bolt carrier group as it is removed from the stock for field stripping. The rod under the return spring is a guide rod that prevents the bolt from rotating during feeding: Once the bolt carrier runs all the way forward it overruns this rod, which allows the bolt to rotate: In an AR-15 the bolt is kept from prematurely rotating by having the cam pin drag against the upper left inner side of the receiver. The tavor must have this system with the guide rod because the cam pin is stationary with respect to the bolt carrier. The desert eagle bolt is held forward in a very similar manner: Rather curious, no?
  10. Dear [iNSERT NAME OF COMPANY REPRESENTATIVE HERE], Congratulations! Your company has been selected to partake in a competition to design an aircraft for the Republic of Kerbalia. The competition will be in the form of a fly-off, with entrant designs being assessed relative to each other and the current front-line multirole fighter of the Republic (specifications included in data pack attached hereto). Should you choose to partake in this process, initial development funds of up to 40 000 Kerbalians will be made available to you. Technological limitations being what they are, the use of speculative engine designs (SABRE et al.) will not be accepted as a means of achieving competition goals. The aircraft submitted must be of the multirole fighter type, with the ability to perform a variety of missions while still being able to outfight current aircraft on a 1-to-1 basis. Significant leeway will, however, provided as to the details of the design. If required, a flyable example of the current front-line aircraft will be provided for internal comparison. Submissions must include, at minimum: - A name and internal design number (a prototype designation number will be assigned) - A full list of specifications - A background and detailed description - One or more images of the submission We wish you the best of luck with your undertakings in this regards. Yours Sincerely, Lotho Kerman Head Company Wrangler, Department of Defence, Republic of Kerbalia
  11. AMX-30: A Second Look

    Since the AMX-30 is about to be added to World of Tanks, I thought now would be a good time to take a look at the design. Conventional wisdom would have that the AMX-30 is a sort of retarded little brother to the leo 1. The designs did originally stem from a joint Franco/German tank project, which, like most multinational programs, fell apart when the partners involved realized they couldn't both be in the driver's seat. Actually, the AMX-30 and Leo 1 differ significantly in design priorities. The first surprise from a more careful look at the AMX-30 is that the armor is actually pretty good for the period: (And before Olifant and Xlucine freak about the inefficiency of hull sponsons, here is a picture of a bare hull, which shows that the sponsons are only used to support the turret ring and do not extend the entire length of the hull) Compared to T-54/55: 100 mm @ 60 degrees is 200mm LOS, while 80mm at 68 degrees is 213mm LOS. Over most of the front of the glacis, the AMX-30 actually has slightly better protection than the T-55! The ratio of trigonometric to effective thickness against APDS/AP type threats is about 2 for both of these inclinations: So, for sub 40 tonne vehicles, both the AMX-30 and T-55 had respectable protection on the hull. Indeed, the weak points of both vehicles would be the turret, which had similar LOS thickness, but at less slope and therefore less effective protection against AP/APDS. The extreme slope angle of the hull would also stand a good chance of deflecting period HEAT ammunition, which often did not fuse properly against highly sloped plates. Compared to the Leo 1: We see that, frontally at least, the French tank is much better protected (they're both paper-thin on the sides). Add to this the fact that the AMX-30 had a healthy -8 degrees of gun depression, and it starts to look like a pretty competent design. One of the tricks the AMX-30's designers used to keep the tank efficient and compact was an unusual layout of the torsion bars: (Thanks to Walter_Sobchack for the image) In a typical tank with torsion bar suspension, the turret basket sits on top of the torsion bars and the torsion bar bushings. This creates a dead space underneath the turret basket. The height from floor of the turret to the ceiling must be tall enough for the loader to perform their job (ideally standing, but in some cases crouched), so the height lost to the torsion bars must be made up above the turret ring. This forces the roof of the turret higher, and so increases the total armored volume of the tank, which increases weight. In the AMX-30 the third road wheel swing arm is reversed into a leading, rather than trailing configuration. This leaves a nice big gap where the turret basket can live, which eliminates the wasted space. AMX-30 is, so far as I know, unique among production tanks in using this suspension design. There was at least one Soviet prototype, the Object 277, that used a similar arrangement. While the AMX-30's suspension was unusually compact for a torsion bar type suspension, it was utterly unremarkable in performance. With 278mm of combined bound and rebound, it was essentially comparable to the M60A1 with 292mm. While this was quite a bit better than the British centurion and chieftain, which had utterly primitive suspension that lacked even independently sprung road wheels, it was a far cry from the Leopard 1, which boasted 407mm of independent road wheel travel. Armament and fire control in the AMX-30 was quite modern; even progressive. Unlike the T-55 and hilariously awful and primitive British designs, the AMX-30 had an optical rangefinder. Because the rangefinder had a wide 2 meter base, and because the commander sat behind the gunner, the rangefinder was operated by the commander as a concession to maintaining an efficient ballistic shape for the turret. The commander's station featured a cupola with 10 direct-vision periscopes (or "windows" as they are sometimes called), a ten power binocular telescope, and a counter-rotating override feature. The gunner was given two observation periscopes in addition to the gunsight, and the loader had a generous three periscopes. The vision from the turret of the AMX-30 was, by tank standards, excellent. Primary armament was the OCC 105 F1. This gun was quite comparable to the Royal Ordnance L7 seen in most other Western tanks of the period, except that it had a slightly longer barrel, a compressed air bore evacuation system, and a slower rifling twist rate. The French are unique in their rejection of passive bore evacuators, preferring the older style of compressed-air based system. The German big cats also featured a compressed air bore evacuator, so there is the tantalizing possibility that the French systems are based on that. If this is true, it would be a germ of truth in the myth that the 75mm gun on the AMX-13 is based on the panther's armament. I have not seen conclusive evidence one way or another. The reduced rifling twist rate of the OCC 105 F1 was to facilitate the famously weird Gessner "Obus G" projectile. Obus G, as I am sure everyone reading this already knows, was a shaped charge warhead where the shaped charge rode inside an outer shell separated by a layer of ball bearings. This allowed the outer portion of the projectile to spin while the shaped charge would not spin, as spin degrades the effectiveness of shaped charges. This design combined the accuracy of a spin-stabilized projectile with the HEAT performance of a fin-stabilized projectile. Actually, Obus G was slightly more effective than the M456 HEAT round of the L7. The slow rifling twist of the OCC F1 precluded the use of APDS projectiles. Any APDS projectile long enough to be effective would have too great an aspect ratio to be stabilized by the loose twist of the cannon. However, in the long run this was an advantage, as the slow twist rate proved well-suited to APFSDS type rounds when these were introduced in the 1980s. In another unusual move, the secondary armament of the AMX-30 was a 12.7mm weapon rather than the usual 7.62mm. This, if the user so desired, could be increased to a 20mm autocannon. Not exactly "coaxial," the secondary armament could be elevated to 40 degrees (vs. 20 degrees for the main armament), to be used against helicopters and low-flying aircraft. Prior to upgrades late in its service life, the AMX-30 was let down by that most syndrome of armored fighting vehicles; a dodgy powertrain. Prior to the 1979 upgrade, the AMX-30 had a rather fragile transmission that required a skilled driver in order for the tank to remain mobile. Apart from this regrettable downside of not working, the AMX-30's powerpack was admirably compact and helped keep the overall size and weight of the tank low. Had it not been let down by an unreliable powertrain, the AMX-30 could have been a big success on the export market. More other Western tank designs of the period, the AMX-30 showed excellent design discipline in keeping the tank small and light. Despite the characterization of the armor protection as useful only against small-caliber threats, the AMX-30 boasted frontal protection that was better than the Leopard 1 and comparable to the T-55. Alas, for the majority of its career, the AMX-30 was yet another reminder that in the absence of a robust powertrain no amount of clever design features will redeem a tank. (Would be much obliged if someone would repost this to HAV after re-uploading whichever pictures need re-uploaded to imgur. I am too tired now and CBA)