CMMG Inc. MK9 M4 Complete 9mm Lower Receiver - Blue/Black, Synthetic, Collapsible Stock

At the time I purchased this lower assembly, there were no complete 9mm rifles to be found. I started out with a 9mm upper and tried to convert my .223 lower to accept the 9mm mags using a magazine block. It was finicky to say the least and I had to mess with it a lot and it was unreliable. This lower came available so I purchased it to go with the CMMG 9mm upper that I already had. There was an occasional issue ejecting the spent shells, I called CMMG customer support and they gave me a solution which worked. I would recommend it if you already have a 9mm upper, but I would rather purchase a complete rifle so that it is adjusted from the factory and functions properly.

This lower was used for a 16” build. It was well finished and put together.

Lower arrived quickly and in good shape. Fit my Colt style upper receiver with no problems. Both Colt and Metalform magazines function well. Would buy another with out even thinking about it.

CMMG is known for quality parts. This lower receiver fits a PSA 9mm upper perfectly. Feeds most 9mm ammo without one hiccup. Save $360 and build your own AR 9mm carbine.

Bought it for a custom 9mm build. Paired it up with a Gibbz Arms side charging upper. Other parts were a CMMG ramped bolt assembly, Wilson Arms 9mm barrel, and a Gibbz rifle length free float handguard. Mags I used were AR stoner 9mm mags; 20 and 32 rounders. I had to file a little on the mags to get the bolt to be able to close, however I did not consider this to be uncommon since it was a custom "mutt" build from a variety of parts. Best kind of build! This is only my second experience with an AR, my first being a Windham that I bought in 5.56. The trigger on this CMMG lower was not as crisp as my Windham and it had a small amount of mushy creep. Nothing really bad, expect it will smooth up after some use. All in all the end product I built using this lower produced 1.5" groups at 50 yards and 4" groups at 100 yards from a brand new barrel not yet broken in. This product was my answer to the shortage of .22 ammo. I reload the snot out of 9mm, and so having a considerable supply of components to make it, I built a 9mm to plink with. Like it a lot. The dedicated CMMG lower is nice since I did not want to mess with a mag block adapter.

Fit my RRA upper great. Black Polymer pro mags seem to function well in the 9mm CMMG lower. Like to build another one sometime in the future. Thanks Buds for another great dealer transfer transaction.

Very solid and well made, works perfectly with my RRA 9mm upper. So nice I just bought another one.