CMMG .45 rotary bolt blowback pcc build

[Baltimoreed]

While I’ve built several blowback pcc’s using Olympic Arms bcg and bbl when I saw the clever rotary bolt on the cmmg Guard I was impressed. A clever way to slow down the bcg without using a massive bcg and buffer. I found a bcg and 8 in bbl on Optics Planet. I had a dpms upper, handguard and a complete lower from my MP5 build. Put it together Saturday and started working out the kinks. I had occasional fte’s so I contacted cmmg cust service. The gentleman sent me detailed drawing so I fired up my mini mill and enlarged it from .500 to .630. Mo more fte’s. Then I started getting feed jams where the bullet was hanging up on the bottom sharp corner of the ramp. I used some fine grinding compound to break the corner and polish the ramp which solved the problem. Today I experimented with a target load .45 and it ran like a champ. No recoil, no forward impulse and it’s so light compared to my others. Might have to get a rifle bbl before it’s over with. I will load some more tonight and try again tomorrow.

3.0 gr of Bullseye 200 gr rnfp PC was too light and I had a few fte but 3.5 gr seems to feed and eject fine.

[3leggedturtle]

How much lighter than comparable blowback? Main reason i dont own an AR in 9mm is the weight.

[Lloyd Smale]

ive got a 16 inch 9mm cmmg ar and if you closed your eyes youd never tell the difference between it and a 556. If it weights more it sure doesn't feel like it. That said a blow back pistol bolt is heavier but by the time you slap in a 30 round mag of both youll never notice. The other 9mm ar I have is a 4.5 inch psa pistol I built. Obviously its lighter the any other ar I own. I actually was thinking on one of the cmmg complete pistols in 45 but talking to them they said they might be finiky with cast and im not dropping 1500 bucks on a finiky gun. By the way my old cmmg 9mm eats ANYTHING and if it has jammed or missfed I sure don't remember it. Matter of fact its probably the most reliable ar15 ive ever owned. My guess is there service dept was being over cautious and covering there buts saying they wont run cast. Now my psa 9 has been a challenge. It runs real well now but its not a gun for someone that doesn't understand tuning and wants a gun that runs out of the box.

How much lighter than comparable blowback? Main reason i dont own an AR in 9mm is the weight.

[bronte454]

I’m wanting to build an AR45 I’ve built 2 556 1 24” and 1 16” . Been reading A LOT and haven’t convinced myself I can tune the the if something is wrong .

[Gtek]

I just assembled a 9mm Stern Defense 10.5" kit on an AR pile of new Anderson pieces. 2.0 KAK, 10" guard and with the can on it still feels just like the 300 and 556 pistols here. MAYBE get to warm it up this weekend, we will see. I was very impressed with quality of fit and finish and I hope it shoots as well as it feels. That rotary bolt idea is pretty clever, keep us informed please.