5.7 AK

1959 Views 36 Replies 15 Participants Last post by 1biggun, Mar 12, 2011

hcpookie

Discussion Starter · Apr 20, 2010

I am getting hold of a PILE of brass and I only have the wife's P90. SO I'm thinking about how to get the 5.7x28 to work on an AK platform. Considering the recent 9mm models from the Izzy factory I'm confident it could be done. Just need to figure a few things out.

I would prefer a gas-operated system even though the original design is that delayed-blowback. Would need a light spring I would think... don't know if any of those .22 springs are still available? I'm not against blowback but the delayed-blowback option is going to take some creative machine work. I could probably put a big heavy spring in the trunion area (thinking automotive valve spring) and cut the barrel's chamber section down to fit inside. Some creative work with a sleeve and *Presto* you have a barrel that floats in the chamber. This would need to move rearward about 1mm to simulate the P90 delayed blowback action. A basic one-piece bolt could be built from there. Just a block of metal with a firing pin and extractor. Heck you could probably make the bolt from mild steel and use a hardened metal insert for the actual "face" of the bolt so as to keep it easy and affordable.

5.7x28 = .223 sized barrel with a different chamber. I could use one of these old Galil barrels

The P90 magazine could be used in a Bizon-style format where the bottom of the receiver is cut away to allow it to mate into position in the magwell. Ejection would be normal side-ejection unless I wanted to get really unconventional and mount the magazine on the side for a downward ejection.

Magazine catch would need to be polymer/plastic to avoid damage to the magazines. Don't think a metal magazine catch would be a good idea.

Thoughts? Would a standard AK gas system be able to be downsized enough to support the small caliber? Any reasons NOT to use a gas system?

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Coils

· #2 · Apr 20, 2010

I think it could be made to work with a gas system, I'd think it would have to be short. A lighter carrier system would help too, DoubleTapMe did one up recently in x25 and has a thread on the Weapon Guild with pics. Here's the thread, hope it works. (edit to add, here's a pic of his carrier)
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On Wikipedia they show this round gets up to 50,000 psi, so I think it would have enough to operate it, just need to figure out how to set it up to use the available pressure.

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muttman

· #3 · Apr 20, 2010

What is the reason for the delay/lock on this build? Muttman

patjsimpson

· #4 · Apr 21, 2010

DoubleTapMe did one up recently in x25 and has a thread on the Weapon Guild with pics. Here's the thread, hope it works. (edit to add, here's a pic of his carrier)

I idolize that man!

Rahatlakhoom

· #5 · Apr 21, 2010

patjsimpson said:
I idolize that man!

He sets the bar high.
Took me 2-3 years to comprehend his applications.
Absolutely pure gunsmithing...priceless.
:rockin:

Do the gas op Pookie.

Coils

· #6 · Apr 21, 2010

I idolize that man!

:notworthy
yeah really, he thinks up the stuff that others copy.

What is the reason for the delay/lock on this build? Muttman

It allows the pressure in the barrel to drop off some before the bolt starts to move.

Viper Dude

· #7 · Apr 21, 2010

Hello HC,
How about something more original ??? Using AK pieces a simple blow-back bolt and an op-rod that the gas pressure pushed FORWARD to resist early bolt opening. This revisits the WW-II VG-1 carbine and later H&K P-7 Squeeze Cocker pistol gas delay concept.

Parts can be made from modified AK pieces and weldments. The slick-coated 5.7 FN ammo seems suited to delay-blowback operation without a fluted chamber. The standard AK piston appears to be nearly ideal for reverse activation. An adjustable gas valve is a good design idea too especially if the gas port is located near the barrel chamber throat area ala the P-7. A backwards FAL FSGB may be simplest to use. Fun Stuff !!!

VD

Runaway Shortbus

· #8 · Apr 21, 2010

^^^
That is brilliant, freakin brilliant!

mrtank

· #9 · Apr 21, 2010

You could trim a standard 7.62x39 bolt back and cut the face for the smaller pocket. It would reduce the strength of the bolt. This would also have the side benefit of having the barrel further back in the trunnion. Could help with feeding. Would be neat with a skeletonized bolt carrier, and a captive piston short stroke gas system like used on the cz58.

Gas-delayed blowback is neat, but they tend to require tight tolerances that tends to have it's trade offs.

Could do something like this.

Talked about in this thread. iB::Topic::Interesting recoil operated/blowback design.

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hcpookie

Discussion Starter · #10 · Apr 21, 2010

Coils said:
I think it could be made to work with a gas system, I'd think it would have to be short. A lighter carrier system would help too, DoubleTapMe did one up recently in x25 and has a thread on the Weapon Guild with pics. Here's the thread, hope it works. (edit to add, here's a pic of his carrier)
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On Wikipedia they show this round gets up to 50,000 psi, so I think it would have enough to operate it, just need to figure out how to set it up to use the available pressure.

Wow, he really chopped that one up didn't he. I must say that more cutting was done to that than it would have taken to just build a new carrier from scratch! :rofl:

To be honest, the more I think about it the more I think a standard gas system would be better than a retarded blowback (I mean DELAYED blowback...) system

I've never been a big fan of blowback anyway. Due to the light nature of this cartridge it will be more like a 7.62x25 build than anything else. Heck its just a brainstorm right now, I may not do it for some time.

I dug around and found a chunk of a hardened shaft (assuming it to be an old car axle) that will be big enough for a one-piece bolt/carrier after I square it up. I'm still going to build a 9mm Bizon build so I may just do both at once. Can't have too many AKs anyway

OK where to find a reamer?

Coils

· #11 · Apr 21, 2010

I must say that more cutting was done to that than it would have taken to just build a new carrier from scratch!

:lol:

kernelkrink

· #12 · Apr 21, 2010

Delayed blowback is also accomplished with a stiffer spring and heavier bolt assembly. HK sez their .308 models would require a bolt of 30-something pounds to function as a pure blowback, they just use the roller system to scale it down to a manageable size. As long as the bolt assembly in your rifle is significantly heavier than the one in the P90, you should not experience premature opening of the bolt.

hcpookie

Discussion Starter · #13 · Apr 21, 2010

Kernel I totally understand where you're going with that. Looking more at my P90 springs and overall design it is certainly feasible to believe a heavier spring will do the job. I'm still thinking that a gas system (admittedly with a very small gas port) will be the best overall approach just for the sake of reliability. If I do use this old Galil barrel, the original gas port will be an obvious starting point and I'll just have to see what kind of gas block I can conjure up.

Still though I don't see reamers available to rent at the normal places, so that may put a damper on this for now.

Rhino_66

· #14 · Apr 22, 2010

Jerry,

I've got a couple Vizio files to send you that apply to this. Let me see if I can find them for you.

.

kernelkrink

· #15 · Apr 22, 2010

Make your own reamer. Back in the old days of wildcatting gunsmiths made all manner of improved chambers with "half reamers". Essentially, they just turned a piece of drill rod to the shape of the chamber they wanted. Put it in a drill press running slowly, heated to red then quenched by running the quill down into a can of oil or water. They then ground away half of it, leaving a single cutting surface. It cuts slow, but for a one-off project and no commercial solution it is about the only way.

Viper Dude

· #16 · Apr 22, 2010

Take it from the Kernel !! Those reamers are also called "D" reamers. You grind away a little bit over half the thickness to provide a cutting edge.

VD

hcpookie

Discussion Starter · #17 · Apr 23, 2010

Yeah I don't have a problem making one, I suppose I could make a casting from the P90 barrel. I can probably making several blade cuts like a normal reamer since I have an indexer now

What would be the best way to convert a .223 barrel? Just do like with the 7.62x25 builds and plug the chamber then ream the plug?

I think for the plug in the .223 chamber I would have to use the cut-off end of a barrel so the threads align, then just ream that out. If I don't, there will be about half of a .223 cartridge in length of "freebore" (no rifling) between the mouth of the cartridge and the beginning of the threads. Again, thinking about using one of these Galil barrels I have...

Note the size difference:

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Viper Dude

· #18 · Apr 23, 2010

Hello hc,
That 5.7 round looks a lot like a non-tapered case !!! Maybe that's just the camera angle. I wonder how the 5.7 would function chambered in a .22 RF barrel ???

VD

hcpookie

Discussion Starter · #19 · Apr 23, 2010

Viper Dude said:
Hello hc,
That 5.7 round looks a lot like a non-tapered case !!! Maybe that's just the camera angle. I wonder how the 5.7 would function chambered in a .22 RF barrel ???

VD

If you mean .22 Rim Fire then no it won't work as the pressure is too high. It is rated for 50,000 PSI which is over 2x that on a soft .22 barrel. Furthermore, it is assumed on other forums that a .22 Hornet action may not be strong enough to handle this round.

Actually I learned right here on Gunco that .22 barrels are "not" your standard gun barrel and are usually not even hardened steel. Looking at some of the carbon fiber barrels with inserts you can understand how little pressure the round needs.

The 5.7 has VERY little taper, if any. No I have not considered using drills to make the chamber

vz58

· #20 · Apr 24, 2010

my case is a non tapered bottlenecked case

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