9mm AR Upper

[samson7x]

I am interested in buying an upper chambered in 9mm for plinking and my local dealer has a CMMG kit for $579. Does anyone have this upper or can you recommend another one? I would prefer one that is threaded 1/2 x 28 for a suppressor that I am waiting on.

Thanks!

[Bitter Bastard]

I can't comment specifically on the CMMG uppper but in general, CMMG is pretty well thought of. Good catch about the muzzle thread pitch, Colt standard is 1/2x36. Are you building a dedicated 9mm rifle, or just want to swap uppers with a 5.56? I just want to make sure you are aware of a few changes to the lower parts group that may be required as well.

Yeah, I know, another posting on the internet that doesn't exactly answer the question.

Bitter Bastard

[samson7x]

Originally Posted by Bitter Bastard

I can't comment specifically on the CMMG uppper but in general, CMMG is pretty well thought of. Good catch about the muzzle thread pitch, Colt standard is 1/2x36. Are you building a dedicated 9mm rifle, or just want to swap uppers with a 5.56? I just want to make sure you are aware of a few changes to the lower parts group that may be required as well.

Yeah, I know, another posting on the internet that doesn't exactly answer the question.

Bitter Bastard

Thanks for the post. I was afraid of the thread pitch issue. I had read somewhere that it wasn't 1/2 x 28 which I don't really understand. AAC doesn't make an adapter for the .45 can to that thread pattern. That poses an issue if the barrel length isn't long enough for me to allow for cut/rethread. I intended on swapping uppers with my 5.56 for the time being until I could acquire funds for a dedicated 9mm lower. I'm only aware of the need for a magazine adapter with different mags. These aren't permanent modifications, are they?

[Bitter Bastard]

Colt uses a different thread pitch for their 9mm's so people don't accidentally put a 5.56 flash hider on it and obstruct the bore. Others mfrs use the usual 1/2 x 28. You'd be best off asking each maker before purchasing to ensure what you are getting. I'd be surprised if AAC won't make a thread adapter for you even if it isn't cataloged. If they won't, I'm sure someone would. You can try over on www.subguns.com for more info on adapters and such.

As far as other changes to the lower, nothing that is permanent by any means. You need the mag blocks obviously, there are too many styles out there to go into. The bolt hold open may or may not need to be swapped out depending on the mag blocks. The hammer may need to be changed also. The DPMS profiled ones will work fine for both 5.56 or 9mm. I think if you get a "ramped" 9mm bolt, though, it will work with any std hammer. Not sure on that, I have a Colt upper and just use a Colt hammer.

And then the buffer and spring need to be 9mm, although some people run std 5.56 parts without problem. I'd be leery of that, though.

Good luck and let us know what you decide to go with and the details as far as hammers, mag blocks, threading, and so on. After looking at all the options, I went with a dedicated 9mm AR with pinned in mag blocks. Just easier that way, except to the bank account.


Bitter Bastard

[Tom Freeman]

Get one with an enhanced/modified carrier. If you dont, it is hard on hammer pins and you can break them.

[Munch520]

Is suppressor compatibility the reason you haven't looked into a 22 conversion? If you already have an AR-pattern upper it'd be a heck of a lot cheaper on ammo and the conversion itself ($160 IIRC).