AR-15 in .357 Sig?

[Caster]

Think it would be worth it? I mean it shouldn't be too difficult. I have a lead on .357 Sig once fired brass by the five gallon bucket for cheap. I'm not interested really in getting into shooting the cartridge in a handgun, but in a carbine, the Sig ought to be pretty stout.

9mm barrel, .40S&W bolt and Lone Wolf even makes a Glock magazine dedicated lower.

Any thoughts?

[Jonnin]

Should make a nice gun. However, you handload. And, you seem to have plenty of experience. And, you said you wanted to consolidate calibers. Tell me you cannot, if building the gun from parts, make it a 9mm with stouter parts and just load your 9mm as hot as the sig caliber? I do not know if that is possible, but I think it would be if done carefully --- the so-called +p+ 9mm is very close to the sig round already and is safe to shoot in well made guns. The only thing I am going on here though was your earlier post about reducing down to a few common calibers. If you want this project, it sounds fun and the result would be very nice IMO.

[Dolomite_supafly]

It would be really easy. Grab a built 9mm upper and run a 357 Sig chamber remeamer in there. After that take the bolt and remove the extractor. Chuck it into a lathe and open up the bolt to accomodate the .424" rim diamter of the Sig round. I suspect you wouldn't even need to touch the extractor. The only thing you might need is a heavier buffer. I would almost be willing to bet the 9mm stick mags would work fine as well just with a smaller capacity.

Dolomite

[Caster]

Well, what you say is absolute truth. I'm only exploring the option because I know a prominent group of people in my area that use the .357 Sig and I may be able have a brass source. As much as I would love to Run for the hills as Bruce Dickinson would say, I know I forever tethered to this area, despite the damnable misery of that, why not make use of ALL of it's resources?

[Caster]

It would be really easy. Grab a built 9mm upper and run a 357 Sig chamber remeamer in there. After that take the bolt and remove the extractor. Chuck it into a lathe and open up the bolt to accomodate the .424" rim diamter of the Sig round. I suspect you wouldn't even need to touch the extractor. The only thing you might need is a heavier buffer. I would almost be willing to bet the 9mm stick mags would work fine as well just with a smaller capacity.

Dolomite

That do make it sound even better. Heavier buffer, maybe a hydraulic buffer and an M16 bolt?

One thing and this is a really dumb Q, but I have ZERO experience with a pistol caliber AR. Are they gas operated? Olympic Arms website shows a pic of their bolt and it don't look the same, I don't see any kind of locking lugs. Personally, if it doesn't lock up, I'm not playing. I'm just not interested in any straight blowback action.

[mikegideon]

I think that caliber has way too much snort to even work with straight blowback. I don't have personal experience, but have always thought that the pistol caliber AR's use the same DI gas system as the .223, but with heavier buffers.

[Caster]

That was my thinking too, but I'm wrong so often, I quit assuming anything.

[Chucktshoes]

I don't know about other pistol calibers (though I assume they operate the same) but I know the 9mm AR is a straight blowback operation.

[Caster]

I'm going to have to take a look but I think it's entirely possible to open up a .223 bolt to .424. That would only be about .024-.025 per side[48-50 thousandths total] then gas operation would be a sure thing.

SAY, anyone got a totally screwed .223 bolt that I could practice on? Burnt, cratered, blown, worn slap out. It would be nice to have a junker to set up on and make a practice run.

[mikegideon]

I don't know about other pistol calibers (though I assume they operate the same) but I know the 9mm AR is a straight blowback operation.

They probably all are, then.

[Caster]

They probably all are, then.

Won't be if I build one. Operating around 40K PSI....I like locking lugs myself;)

[Dolomite_supafly]

Up until recently all 9mm AR's and other pistol calibers were blowback. There has been a trend of making DI or piston uppers for pistol calibers.

There are several custom builders that are making several pistol caliber AR's that are gas driven. From memory they make them in 7.62x25, 9mm, 10mm and 45 ACP. 357 wouldn't be any different to build. I do know they require a gas tube that is way shorter than even a pistol length gas tube. Of the non standard DI builds I have built I have done a 7.62x25 but never got it to run 100% so I had it chambered it in 7.62x39. After that it was 100% reliable with factory ammo as well as using my 180 grain loads.

I do know from discussions that gas driven pistol caliber AR's have very little recoil, compared to blowback guns, because the it soaks up a lot of the recoil. It is also very tunable to increase reliability and decrease felt recoil. It also makes for a cleaner system than blowback whether using a DI or piston setup.

Here are some discussions on gas driven pistol caliber AR's:

http://www.ar15.com/forums/topic.html?b=3&f=15&t=366336&page=6

http://www.ar15.com/archive/topic.ht...&f=15&t=509364

Here is one of the more prolific custombuilders:

http://www.teppojutsu.com/

Ron Williams is another builder that does an equally good job building custom AR's. I do believe this is his 7.62x25 DI AR:

http://www.cncgunsparts.com/ar-15_m-16_762x25_uppers

I have had more positive dealings with Ron than with Teppujitsu. I asked Teppu if his system would work with subsonic 7.62x25 rounds and his response was "buy one and find out". A few other general questions resulted in similar responses.

I have provided Ron, through a mutual friend, with some of my subsonic load data I worked up. He has also provided me with some data as well, again through a mutual friend. I also worked on what twist rates where needed to get a subsonic bullets to tumble in the 7.62x25. I did this for a friend of both Ron's and I's.

I also have a 9mm blowback I built from a parts kit. Nothing out of the ordinary and anyone could have put it together. It uses a standard 5.56 carbine buffer and is 100% reliable with everything except a few HP styles. I do know that blowback guns kick a lot harder than a gas gun even when the DI is a much heavier caliber. The 9mm kicks substantially harder than my 223 gun which happens to be lighter than the 9mm as well.

I have done several blowback 7.62x25 AR's for myself. I didn't like them because they were loud, dirty and actually painful if you did a lot of shooting. After a few hundred rounds I would have bruising because the gun only weighed around 5 pounds and had quite a recoil impulse. Ultimately I gave up on the 7.62x25 AR's and built bolt guns because I was more interested in shooting subsonic rounds but still wanted the ability to shoot surplus.

Dolomite

[Dolomite_supafly]

One more thing, opening up the ,378" bolt up to .424" isn;t a problem. I have had them opened up to .445" for the 7.62x39 without issue. The only issue I have seen is the extractor is too far in and will not snap over the rim. To remedy this a setscew was installed that allowed me to set the extractor depth.

Dolomite

[50 cal]

Olympic makes .40 cal bolts. I have one they shipped me by mistake when I ordered a spare 9mm AR bolt. I ordered another bolt and kept the 40cal bolt thinking I might do a .40 or a .357SIG AR. Haven't done either.

If you want the bolt, I'll sell it to you for cheap.

Shouldn't be a thing wrong with a blowback .357 SIG AR, there are plenty of .357SIG pistols. A blowback rifle shouldn't matter a bit.

[Caster]

Well, I want to say thanks, this has been a fun discussion, but my potential brass source turned out to be a bust. Everything was contingent on a very cheap brass source and without it well....I won't say I'm scrapping the idea, but it's certainly back burner. Besides I have been wanting to build a .300 AAC Blackout anyway.