roguetechie

I was finally able to find a place that actually had a couple boxes of 7.5X55 Swiss. Now I finally have gun food for my impulse buy K31 that I purchased last year. It's the Hornady stuff loaded for Graf & Sons and was perilously expensive at $32 a box.
I've noticed that the PRVI Partizan stuff is available again at a variety of online outfits and I'll probably pick up a hundred rounds or so in the future.
I am so tempted now to bring that K31 up to Alaska as the bear rifle...

Seriously?


I have C&C Generals vibes from this thing.

Typhoon-K MRAP

Earlier i reposted some pics of moded SVDs from russian edition of Populat Mechanics, here is forum discussion with creator:
http://forum.guns.ru/forum_light_message/2/1723231.html

Walter, 
I have the blueprints for the Canadian 7.62 NATO M37retrofit if you want them let me know.
Sidenote: the Browning 1919/m37 is just outright an awesome gun that you can get to run just about any round between .22 lr and 8x63 Bofors...
Including 303 & x54r... I helped a buddy do a x54r version...
Fun fact: the Finns even figured out a really simple push feed link to convert mg42's to x54r... Aimo Lahti was a genius.

*cracks fingers*

Something that has interested me for a while, are shape stabilised projectiles. As in, projectiles that are stable due to their shape. Everybody has heard of rotation stabilised and fin stabilised projectiles, but shape stabilised is kind of different. I guess most of you here have seen shape stabilised projectiles without actually knowing how and why they work.

Geek sidenote: Fin stabilised projectiles are actually fin and rotation stabilised.

As I said, shape stabilised projectile have a stable flight path due to their unique shape.

Figure 1: A 84mm Carl Gustav shape stabilised HEAT-round

Note the slightly ogive front and the stand-off, which are characteristic of shape stabilised projectiles (SSP). Both features are absolutely crucial for the SSP to work.
I'm going to throw you guys into the deep end by showing a .gif of the airflow in front of an SSP.
Here's a link because I can't embed .gifv apparently
The first thing you should notice is the air circulating in some-sort of pocket, and that this airflow is subsonic. Before I continue, here's the airflow in front of a blunt projectile: Clicketyclick
While that projectile has a subsonic airflow in front of it as well, it is not circulating.

Here's the airspeed of both projectiles as a normal picture:

Figure 2: Airspeed in front of an SSP


Figure 3: Airspeed in front of a blunt projectile

It's clear that an SSP has a ogive-shaped subsonic airpocket in front of the projectile. This basically emulates the ogive of a normal rotation stabilised projectile. In other words, it makes it more aerodynamic. But does that airpocket stabilise the projectile?
No it does not.

So why is this projectile stabilised? The key is in what happens when it starts to tumble. Right now, there is nothing stopping the projectile from tumbling, and that's the interesting thing. There is literally nothing stopping the projectile from tumbling, except...


the projectile itself.

Lets take a look at what happens when an SSP starts to tumble. (If I remember correctly, I rotated the projectile 10 degrees)
First off, the airflow in front of the projectile. It's fairly obvious that the airflow has changed. Lets check that again, but this time as a picture.

Figure 4: Airflow in front of a tumbling SSP

Again, it's obvious that the airflow has changed. The subsonic pocket has mainly shifted to one side and the air itself isn't really circulating in the pocket. This change causes a huge change in the Cd of the projectile. Let me show you why.

Figure 5: Pressure in front of a tumbling SSP

Next, the pressure in front of an SSP flying straight.

Figure 6: Pressure in front of an SSP flying straight

Please note the approximate pressure in front of both projectiles. The tumbling projectile has, on one side, twice the pressure as the projectile that's flying straight. Very interesting. What's even more interesting is that the pressure occurs on the opposite of the side it's turning to! The projectile is turning upwards, but the pressure builds up at the bottom. This pressure forces the projectile to start turning down again, forcing the projectile in a state where the pressure on all sides is equal.

Voila, a shape stabilised projectile.


But... why does it work?

The subsonic airpocket is created by the stand-off and that little flange, or whatever you want to call it. The dimensions and placement of both are equally important. The stand-off and its side create the airpocket and the flange give the airpocket the required shape. The stand-off size can vary, but the flange size and placement is very important. If the flange is too far forward or too far back, the airpocket will be either too small or too big. Why does the size of the pocket matter? Because of this:

Figure 7: Subsonic pocket in front of an SSP

I changed the parameters slightly and made all airflow above Mach 1 red. Whatever is not red, is trans- or subsonic. The interesting thing to note here, is the pocket extends to the edge of the projectile (if I made the projectile better it should be exactly on the edge). (Sidenote: Here's the same picture of an SSP at a 10° angle)
While the airpocket does not start at the flange, the flange determines where the pocket starts. If, at this velocity, the flange was further back, there would be supersonic flow hitting the front of the projectile, massively increasing drag. If the flange was further forward, the airpocket would be further forward too. This would mean the airpocket would not end at the edge of the projectile, but further out. Creating an airpocket which is wider than the projectile. This would allow the projectile to tumble a bit, because pressures wouldn't change much unless there is supersonic flow hitting the projectile.

It is also possible to change the size of the airpocket by changing the front of the projectile itself. If the radius connecting the front and the stand-off is too big, the airflow inside the pocket would disrupt the circulation. The same would happen if the radius is too small. The angle of the front is important as well, but I haven't expermented that much with it so I don't know how important it exactly is, but it has an effect on the airflow.

By the way, if the flange did not exist at all, the airpocket would start at around a third to half of the stand-off. Which would completely ruin the airpocket. Without a flange, the stand-off itself would have to be way bigger and longer to create the same kind of airpocket.

But Bronezhilet, I hear you cry, if the airspeed changes, the pocket changes as well!

I'm glad you brought that up, because you are right.

A shape stabilised projectile only works properly within a certain flight envelope. If the projectile is moving too fast, the airpocket would compress allowing supersonic flow to hit the front of the projectile. Which in turns increases drag. By a lot. If the projectile is moving too slow the airpocket widens, allowing the projectile to tumble a bit before it would stabilise.

I've been brainstorming with Colli a bit, and we've come to the conclusion that is why some projectiles are both shape stabilised and fin stabilised. When the projectile is moving too slow for shape stabilisation, the fins would keep it pointing in the right direction.



And that concludes today's lesson. Thank you for reading.

Type 96A gunner sight

Colli & Zyklon,
I can actually answer this for you guys conclusively. Colli's hypothesis/suspicion that this technique wouldn't work on most Otto cycle engines is 100% accurate. 
Basically the only engines you can use this technique against are pre distributor cap era carbureted dinosaurs... Magnetos and points are the cause but I am not recollecting exactly why.  More or less tthough it's because they pump out a shit ton of dirty rf noise across huge chunks of the spectrum.
One of the reasons this was the preferred methodology for this application has to do with c119 flying boxcar and EARLY c47 gunships flown by people who weren't there, out of countries we weren't in, and thus these very deniable and fungible assets were better off with a detection setup that so plausibly deniable.

While looking for information on perforated armour, I bumped into this:
http://www.abovetopsecret.com/forum/thread162738/pg1
 
This shit is why it's so disappointing to discover that all the secret armour out there is essentially NERA. Look at the description of chobham: layers of high-hardness steel and advanced ceramics! With kevlar fibre-reinforced back plates! And a strike face of ultra-hard, ultra-tough DU/tungsten alloy! It all sounds so space-age and high tech - the penetrators just bouncing off this magic stuff as the crew no doubt hangs out of the hatches, laughing maniacally.

I'm so glad to know there's at least a few other 20 inch bbl a4 style setup or before fans out there .. I'm kinda one of them too, however my fetishistic ideal seems to be for guns that are more diemaco c7a2 than the more staid and conventional a1-a4

To be fair on the whole bore axis thing, a low enough bore axis in conjunction with a pistol specifically designed to take advantage of it can actually provide real and tangible benefits for the user.
This is why things like hammerli .22 target pistols and stupidly expensive hand crafted and bespoke European pistols in larger center fire chamberings often sport very low bore axes.
There's actually a pistol "design" that I hope to someday do an actual real and working version of one or both of the embodiments shown in the patent and nonfunctional display models the designer showed at the shot show around 2 decades ago. The "designer" was a character named Raphial Morgado, he's since moved on to flogging his Massive Yet Tiny engine. Just like his pistol "designs" and the "revolutionary" ammunition he "invented" to fire out of it the engine is not only vaporware, but also far from a new original or "revolutionary" concept.
In the case of his ammunition concept, it was just a modernized and smokeless powder using ripoff of the rocket ball... Except for the whole thing where rocket ball ammunition actually works.
The two versions of the pistol he was intending to fire the ammunition from is actually the interesting part. (Taking what's in the patent application and turning it into a functional firearm which uses standard non caseless ammunition will obviously involve a nearly complete redesign of course but the resulting guns could potentially be interesting or even really awesome)
Basically though the pistols have their detachable box or tube magazine above and parallel to the gun barrel with the cartridge bases down. This makes for a potentially extremely tiny package theoretically making something with glock 17 magazine capacity and barrel length in damn near single stack glock 380 size envelope!
Or, in the tube magazine version which is meant to fold in half for concealment you're looking at single stack glock .380 barrel and ammunition capacity in a package almost as small as the absurd .22 magnum NAA derringer revolver.
You can probably see why the thought of this excites me...
If someone pulled it off and got it to work well and etc it really could be very useful, especially for issue to deployed soldiers as an always on them defense against the whole green on blue / sudden jihad syndrome bullshit that is really the only reason left to keep in inventory and issue pistols to western military personnel.

Is it good time to post this?

Per Xlucine's proposal, the turret would be longer, but either narrower or lower from the front.  It would be harder to hit from the front, but easier to hit from the side.
 
Protecting the sides of the turret from hits from the front from, say, a 30 degree angle is not difficult; ERA is very good at this, and ERA is cheap and insanely effective considering that it is tiny and light.
 
Reclining driver's position would probably lengthen the hull, so you would get more side area exposed.
 
I don't think there's any way to shrink any measurement of a T-64/T-72 style tank without growing some other measurement, unless you accept a smaller gun/engine/armor, or unless technology allows you to miniaturize one of the components.

I dunno if this belongs here, but as soon as they reached the chessboard I was riveted:

"Improvised Employment of S-5 Air-to-Surface Rockets in Land Warfare: A brief history and technical appraisal"

Really quick and violent displacement after firing?
Either that or he's using the optic and the additional height to try and spot the enemy.
I like the really quick displacement idea better.

Azovets i alive. Photos from testing of that thing.

The Uziel Gal rifle is on of my favorite might have beens as well.
Unfortunately after rage quitting the first in the series of two videos that are out there about it three times, I've basically accepted that I'll never really get to learn much more about it.
If they hadn't hired porky pig to be the video host, I could probably learn more about the guns.

Hey thanks guys!
It's nice to feel welcome somewhere, suffice it to say that other places I go I get the distinct feeling that every time my name shows up other places a whole forum shakes their heads and says oh Jesus not him again in unison.
Hopefully I'll have some medium exciting things to drop in the gun pron thread shortly.
The wife has conditionally approved some expenditures, provided that the auction gods favor me, this should result in some acquisitions at post election panic low low discount prices.
Assuming that the stars align, and I don't hate my own work too much to post it, you'll probably see my take on what the Gwinn arm gun could've been as well as some creative uses of cz-26 parts kits etc.

Ok,
If forced to choose between the first two options, I'd take an SKS every time.
FWIW, I own an SKS and an inherited Winchester 94 so I could actually choose between the two.
Personally though, I'd take a vz52 if I could just to be different.
And because vz58's with 30 round mags suck to go prone with...
Sorry Don,
I know us PNW people should stick together, but I'm just not a lever gun guy. Mostly because I never found a source for $179 parts kits, nor can you make lever gun receivers with harbor freight shop presses.

Hey thanks guys!
It's nice to feel welcome somewhere, suffice it to say that other places I go I get the distinct feeling that every time my name shows up other places a whole forum shakes their heads and says oh Jesus not him again in unison.
Hopefully I'll have some medium exciting things to drop in the gun pron thread shortly.
The wife has conditionally approved some expenditures, provided that the auction gods favor me, this should result in some acquisitions at post election panic low low discount prices.
Assuming that the stars align, and I don't hate my own work too much to post it, you'll probably see my take on what the Gwinn arm gun could've been as well as some creative uses of cz-26 parts kits etc.

Hey thanks guys!
It's nice to feel welcome somewhere, suffice it to say that other places I go I get the distinct feeling that every time my name shows up other places a whole forum shakes their heads and says oh Jesus not him again in unison.
Hopefully I'll have some medium exciting things to drop in the gun pron thread shortly.
The wife has conditionally approved some expenditures, provided that the auction gods favor me, this should result in some acquisitions at post election panic low low discount prices.
Assuming that the stars align, and I don't hate my own work too much to post it, you'll probably see my take on what the Gwinn arm gun could've been as well as some creative uses of cz-26 parts kits etc.

Hey thanks guys!
It's nice to feel welcome somewhere, suffice it to say that other places I go I get the distinct feeling that every time my name shows up other places a whole forum shakes their heads and says oh Jesus not him again in unison.
Hopefully I'll have some medium exciting things to drop in the gun pron thread shortly.
The wife has conditionally approved some expenditures, provided that the auction gods favor me, this should result in some acquisitions at post election panic low low discount prices.
Assuming that the stars align, and I don't hate my own work too much to post it, you'll probably see my take on what the Gwinn arm gun could've been as well as some creative uses of cz-26 parts kits etc.

I think the Mini-14 and Mini-30 would be more popular if the mags were less expensive but reliable.
People will over spend on an over-priced rifle and not bat an eye.
But there'll be hell to pay if they have to shell out an extra ten bucks or more on magazines.