Currently I have a 10mm AR pistol made by CMMG and love it!  Curiosity  has me wondering if anyone makes an upper in 357Sig that would work with my current lower?  My current lower uses Glock mags and has a BHO so the only thing to change would be the followers in the mags and a new upper, anybody do this or know of an upper that would work?  Thanks!

I’ve pondered this too. I can’t remember who, but I remember seeing a 357sig gas gun. Always thought it’d be a phenomenal gun to shoot in an 8”-12” barrel.

I agree an 8"-12" barrel would be great, the better question can any pistol caliber upper work on any lower?

I made a semi-auto Uzi in 357 Sig.

I used a 45 ACP bolt with a 9mm extractor.

That was a perfect fit on the case rim.

I tried 41 AE magazines, but Uzi 9mm magazines worked better and worked well.

I reamed an aftermarket 9mm barrel that wasn't chrome lined.

I did see a Mini Uzi in 10mm before.

In 357 Sig, the expansion of the bottleneck case shoulder put additional rearward pressure on the unlocked bolt.

This was borderline almost failing in the Uzi, but did work.

It caused the rear of the case to bulge some, as it moved while there was still quite a bit of pressure.

40 S&W and 10mm might not have this issue.

Sure - as a single shot.

.357 SIG uses a completely different magazine size than 10x25mm Norma, so you will likely need a different lower.  .357 SIG/.40 S&W/9x19mm/.45 GAP use the original Glock magazine size.  .45 ACP & 10x25mm Norma use the larger Glock magazine size.

Your existing 10mm CMMG bolt might be the ideal bolt for .357 SIG, however.

Since people are shooting 40SW in 10MM Glocks using the 10MM mags, I dont think the mag will be the issue. Sure the loaded cartridge will be a little short in the mag but should work like it does with the Glock pistol.

OP, have you ever tried to shoot 40SW in your 10MM PCC? If that works, then you know it's at least possible to go 357.

Obviously, you will need a barrel chambered in the 357SIG but everything else, including the lower, may work.

Wanna say Rudy @ macon armory can do a DI 357 sig upper for you. Also think Ron Williams did at one point as well.

With a hot cartridge like that I would lean towards a locked bolt setup. DI being the easiest likely.

You could also handload to longer COAL's and really hot rod the cartridge!

Then there's the 9x25 dillon......just saying

W/ Liberty 50 grainers.