Miroslav

Well the FAMAS isn't a bad design. Given that they were going to make their own production line from the ground up, I wouldn't say that it's an irrationally expensive design either. On the modern US commercial firearms market there has been some efforts to make semi-locked or locked bolts for pistol caliber carbines and submachineguns. This lowers felt recoil, ameliorates performance with suppressors and with some larger pistol calibers. SIG has a gas operated, rotating bolt design, but I wouldn't say that it's completely clear that the SIG design is leaps and bounds better than the CMMG radial delayed blowback.

There are a bunch of semi automatic hunting rifles that have solved this problem. The reason for placing the gas system below the barrel is that it fits nicely into the handguard. This makes the rifle keep a traditional and slim profile. In general, they are much lighter than for example the M1 Garand, but they have a lot of small parts and are kind of messy to disassemble. This is afforded by the designers because they have access to modern manufacturing methods, and their customers rarely have to take the rifle apart in a hurry, or in the dark, or in the rain. One positive side effect of this layout is that it moves the recoiling mass down. All of these rifles are sold primarily with traditional stocks, but having the recoiling mass below the barrel somewhat compensates for the lack of an in-line stock.

I've spent a lot of time thinking of how I'd design my dream hunting rifle. I've ended up deciding that it's worth it after all to put the gas system below the barrel. It really creates a whole host of problems. I despise the cuckoo clock engineering on rifles like the modern Browning Bar (not the lmg), but it's hard to move the impingement force from the gas port to the bolt carrier in a satisfactory way. You also don't want a heavy and bulky op rod like the Garand design. And I want the bolt carrier to be easier to get out of the rifle than in the Browning Bar or H&K SLB 2000 (or worse yet - the Remington semi autos).

The nicest design in this category is definitely the Benelli R1. It has a wonky gas piston system it and hides the recoil spring in the stock, like a lot of semi automatic shotguns. It is the only rifle of this kind that has an acceptable takedown procedure. It's not perfect, but for a rifle that can be chambered in .338 Win Mag it is very nimble and nice to handle.

As a comparison, google the youtube video with a guy that takes the bolt carrier out of his FNAR. "FNAR disassembly". Compare that to how you get the bolt out of an AR-15, or an AK, or any other rifle designed without a strong traditionalist aesthetic requirement.

I still admire Amerika for generating so much disposable income among its citizens that they feel like they can afford sinking so much of it into such futile projects.

I'm sorry, my sarcasm wasn't coming through.

This spring is (according to the designer) what keeps the bolt from rotating in the bolt carrier, before it has moved all the way forward to the chamber.

https://ibb.co/K5Xs4zV

<a href="https://ibb.co/K5Xs4zV"><img src="https://i.ibb.co/mRGyZFh/APED.jpg" alt="APED" border="0"></a>

I don't think they'll ever get anywhere with this.

Don't get me wrong. I'm an ignorant fool. I'm not an entrepreneur. It takes courage to go into the unknown and take a chance.

I still think this anti-pre-engagement mechanism is worthy of some appreciative attention. 

I know you all read or write for tfb but here's the link. No time link cuz the whole interview is worth watching.

I really wonder how he funded this thing. I really love how he's passionate, but how will he ever compete with a guy like serbu? 

https://www.thefirearmblog.com/blog/2020/11/18/the-50-bmg-ak-project-as-told-by-brandon-the-ak-guy/

Well, as long as you have a set of premises to keep your definition of "normal circumstances", your formula holds up very well as a general pointer. I still think the factor "3" is high.

There are so many different kinds of tried and tested receiver shortening "crazy BS" design elements availible to a designer that perhaps the formula could be further specified to:

If: R2>3*(C2-C1)+R1

Then: designer is lazy

What do you mean by bolt extension distance? I'm guessing the difference in how far the bolt lugs protrude from the bolt carrier as the bolt is unlocked.

On 9/4/2020 at 5:45 AM, Sturgeon said:

 

[...] Your spring assembly and various other hardware also needs to be longer. Your bolt needs to be bigger and it will extend further too, so that's an additional bit of length, and you can approximate that as an extra increment. Together, that adds up to a 3x modifier. Take it from someone who's designed six rifles lol.
[...]

I could buy the first two increments, but I don't think you should count having the spring in the forend as "crazy BS", and if it's in the forend (or there's just enough space in the carrier to stuff it in there anyway) you don't have to extend the receiver to fit the spring. Also you counted the bolt length twice. And you could have the hammer extend over the rear end of the magazine (or any bolt hold open device), which would save you from having to extend the firing pin all the way from the chamber to behind the rear of the magazine. I think the SU-16 has that configuration, but I'm not sure.

Yeah ok I'll quit the semantical nitpicking. I appreciate the attempt at generalizing. I wonder how well this stacks against the HK roller locked series, or a comparison of Garand/M14/Mini 14.

I've got some CAD models of long guns as well, but I'll keep them to myself for now. I have a PCC design that wouldn't require all that much of a workshop to put together, compared to a locked rotating bolt, gas operated rifle.

Hey Sturgeon, you can't just drop an authoritative statement like that formula and not back it up. Please show us how you came to the number three. I'm genuinely curious. Having this extremely specialized hobby as well, I have a notepad at home with calculations made to the same end. Writing from on top of the loo at the office, I would have guessed at 2 rather than 3. Also, you must need a lot of premises to be valid for it to be true, mainly that the receiver was designed for optimization with regards to overall length.

There are a lot of CAD models of the scar availible online. Check out grabcad. I've got a model on my home pc that is quite accurate, and I think I got it from there. Way easier to measure than counting pixels.

Finally, while I enjoy the high level posting on this forum, I think you're being quite harsh on the OP. Who cares if it's the trunnion or the barrel extension.

Yeah that looks like quite the distance. Is it meant to reduce the angle the cartridge has to tilt to get from the double stack to the center position?

On bolt arrangement: I've been thinking I should go with a six lug bolt, with the lugs arranged like the seven lug bolt on an AR-15. This is inspired by the recessed lug that some manufacturer (I've forgotten which one) uses on the lug opposed to the extractor. As far as I can calculate, this setup is plenty strong. Bolt carrier should look kind of like a .308 AR carrier cut off behind the firing pin and instead of a gas key it has a protrusion where the op rod/piston hits it.

I have some vain dreams of spending a ton of money to have a prototype of this rifle built. As I'm based in Europe, I don't have a cottage industry of AR-15 manufacturers that I could pay to make me a barrel extension with a broach. Because of this, I'd have to CNC mill/lathe both the bolt and barrel extension (and then maybe heat treat and remill, I don't know, not really an expert on metallurgy).

Right now I'm leaning towards making the housing for the bolt catch be less obtrusive, by moving it to the side (with a little arm that reaches in towards the spot where the follower actuates the bolt catch) so that the hammer doesn't have to reach too far to hit the firing pin. I think the bolt carrier/hammer interaction during the recoil stroke will work out. The hammer will be pushed way deep down by the bolt carrier, but I guess you could let it follow the BC by a small bit before it's caught by the disconnector and later held by trigger. This will reduce the distance the hammer will have to travel upon firing to make it to the firing pin. Of course, I haven't calculated the hammer travel speed, so I don't know how big of an effect it would have on lock time, which in itself is not that important. All in all, this would mean keeping the AR style carrier/firing pin. If I can't make a trigger group/hammer that seems plausible enough, without compromising receiver overall length, I'll have to go with a different arrangement for the carrier.

The linear hammer thing is interesting.

Civvie semi autos usually have the bolt catch by one of the front corners of the magazine. I suspect they do that to keep the receiver short. They also often have a bolt carrier that is shorter than the long action ejection port, but with a telescoping dust cover on the carrier.

I found an answer to my own question, that I think could be satisfactory. The ARX rifles from beretta has a cut in the cam pin. The firing pin spring keeps the firing pin in a position that holds the cam pin in place, but if the firing pin is pushed in, the cam pin can be removed. I could do some variant of this.

I also need a way to keep the firing pin from reaching the primer if the hammer is dropped prematurely. With a carrier mounted firing pin, this is not a problem. With a bolt mounted firing pin, this has to be addressed. The M14 has a tab sticking out radially from the firing pin. That tab has to go through a slot in the receiver for the tip to hit the primer, but the firing pin rotates with the bolt, and the tab won't line up with the slot unless the bolt is in the locked position. The whole point of mounting the firing pin in the bolt was to shorten the bolt carrier, so I don't want a part of it sticking out. rearwards to block the hammer...

Any other ways of doing this than adding a bunch of small parts to the trigger group?

Hey mr Sturgeon-sir,

I'm slowly drawing up a rifle design as well, although I'm progressing much slower. It's meant to be in a traditional stock layout, so minimizing the overall receiver length is very important, as it directly increases the length of the entire rifle (unlike pistol grip layouts that let you extend the receiver and occupy the stock area behind the users wrist).

When I reread this thread I found the posts on firing pin in carrier vs firing pin in bolt. I've been going over the same thing over the last days, as I want the carrier to be as short as possible when the bolt is in the unlocked position. I tried to sketch a hammer that would curve over the bolt catch housing, but I couldn't make it look trustworthy. It rotated 90 degrees from the forward to the down position...

Long story short: I don't care about bolt/carrier mass ratio, because I have an op-rod where I can hide the carrier mass. How could you mount the firing pin in a rotating bolt in a more user friendly way than than the M14/AK punch pin? I've thought of having the bolt stem threaded and having the end of the bolt screw off when you want the firing pin out, but if the firing pin holds the cam pin in place, you'd need to screw apart the bolt each time you want to separate it from the carrier. As there's probably a lot of grime and gunk near the bolt, and as it's pounded by the hammer all the time, those threads are probably going to get quite stiff.

.224 valkyrie?

5 hours ago, Oedipus Wreckx-n-Effect said:

That is so weird.  Didn't the Czech Republic kind of hate the soviets?

They still do. Dont mind making money off of them though. I do think its very cheesy, and if I was a czech gun maker I would not make a gun with the hammer and sickle on it.

So B&T are expanding the usw concept to include a stocked polymer frame for the sig mhs pistol.

It's peculiar that they are doing it without the fixes optic mount. I had the chance to talk to an aimpoint engineer last year and I (foolishly perhaps) expressed my scepticism towards the usw, for which aimpoint developed a special micro red dot.

Does anyone know what kind of sales the usw have made? It wouldn't surprise me if this new product sells better than the original, not least because of the price.

Do you know what's up with the B&T USW?

It's a cz75 based pistol with a stock adapter and an specially designed small aimpoint sight. The selling point is that regular police officers can carry it in a holster and, by using the extremely minimal shoulder stock and sight, having a weapon with greatly increased range and accuracy (compared to a regular cz75 shot by a police officer with the regular amount of marksmanship training). This is supposedly going to be a big seller as police adapts to the increased terrorist threat.

Personally, I think it might be a tough sell. The gun is less comfortable to carry than a polymer wonder nine and I'd very much prefer almost any real rifle to this thing, if I was going up against a bunch of crazy people with AK's.

Does anyone know if they're selling any? I think I read on tfb that some Swiss border guard like agency are using them.

Excerpt from a Soviet examination of an MP-28: "The trigger mechanism of the Schmeisser submachinegun is a good example of now not to design a select fire trigger mechanism"

Cool quote! Do you have a source?

Well, if they put the recoil spring around the rod and mounted the rod in line with the bore, then the G3 wouldn't have the hump. If you let the recoil spring and the rear of the bolt carrier group recoil into the stock then I'm quite sure you could fit it in there without having to draft orangutans.

Of course, then you wouldn't have any paratrooper variations of your rifle.

I watched the Forgotten Weapons Gerat06 video again the other day, and I started thinking about that rod sticking out from the bolt carrier. How come the CETME and HK rifles have the rod on top and pointing forwards, instead of rearwards? I don't think they would have had a problem fitting a recoil spring behind the bolt carrier group either way.

http://s33.postimg.org/7zaibaljj/RDBB.jpg

Do you think it could have anything to do with the fact that they really wanted that charging handle manual of arms? By putting the rod forwards, you get this nice cylindrical channel where you can put your charging handle, which makes your big rifle works just like the submachinegun you're already used to. I like this explanation, because it seems reasonable that a design to replace the obsolete bolt action rifles to work alongside not-yet-obsolete 9 mm submachineguns would be designed to have ergonomics matching the submachineguns, to reduce training time for ww3.

If I'm not mistaken, quite a few WW2 era SMG's are reloaded by 1) locking bolt open manually 2) inserting magazine 3) letting bolt forward. The G3 is reloaded the same way. Note that this is one more operation than for example an m1 thompson, m1 carbine, stg 44, ak or other no bolt hold open firearms with detachable magazines. I haven't tried but I don't think you're supposed to load a G3 with the bolt closed. Correct me if I'm wrong.

On the other hand, it seems weird that they would value quick and easy reloads so lowly that they didn't just ditch the old manual of arms and made their rifle easier to manipulate (adding, for example, a bolt hold open, which would go well with magazines that are really hard to insert when fully loaded). That rifle could have a 9 mm SMG to go with it, using the same simple manual of arms. Unless there's some benefit with the extra weight of the taller receiver and charging handle assembly, the design of the CETME/g3 seems a little weird, considering where it came from.