Custom 9mm AR Carbine (PCC)

by on 05/10/2016

Here at TRGRiQ, we are fans of pistol caliber carbines. While some may turn their noses up at them, we recognize their potential. Since the days of the “Old West,” Cowboys saw benefit from having both revolver and lever action chambered in the same caliber. There was an advantage to only having to carry one type of ammo. Today’s modern platforms are more advanced and faster handling. Combined with soft recoil for faster follow-up shots, low muzzle blast in tight spaces and less over-penetration when compared to most rifle cartridges – all make for great CQB work. While there are several variations that have come and gone over the years, most notably the HK MP5 and UMP, there’s one that we particularly like for its familiarity and customizability (it’s a word, look it up).



The Colt 9mm SMG is, as you guessed, a “Submachine Gun,” pistol caliber SBR or carbine chambered in 9mm and is based off the M16 platform. Featuring a 10.5″ barrel and weighed just under 6 lbs. Unlike other Sub Guns, it operates from a closed bolt making it inherently more accurate. Besides the aforementioned, it differs from its 5.56 brethren in that it is direct blowback (not impingement), uses a proprietary BCG/ barrel, and the magwell is modified to accept Colt (UZI) mags. Typically, it doesn’t have a forward assist and features a large plastic shell deflector that covers half the ejection port. Around the age of 15, I had the opportunity to shoot one at a range in Manchester, NH and have wanted one ever since.

Let’s fast forward some years later. The first carbine I put together was, you guessed it, a 9mm AR. This was a more contemporary semi-auto interpretation. It featured a 16″ Rock River Arms upper on top a CMMG lower. Because I live in the People’s Republic of California and a SMG, SBR or pistol were all out of the question. While one of those would’ve been cool, a 9mm bullet out of a carbine-length barrel is ballistically comparable to a .357 magnum. I chose the RRA upper over the CMMG because I’m particular, I didn’t want the forward assist on CMMG and liked that the RRA resembled the Colt. So I took the upper half to local shop, Addax Tactical, had them knock off the A2 and install an A.R.M.S. #41 folding front sight post then chop, crown and thread the barrel at 14.5″ and pin a Smith Enterprise Vortex flash hider. I also exchanged the RRA BCG with ADCO Firearms for a ramped CMMG. I replaced the RRA charging handle with a PRI 9mm Gas Buster. At the time, most 9mm lowers, including the Colt and RRA, were mil-spec forged 5.56 lowers with a magazine block inserted into the magwell enabling it to accept the Uzi mags. These mag blocks were known to be somewhat problematic which was why I went with a CMMG MK9 dedicated receiver. This forged receiver’s magwell is machined to accept Colt pattern mags without the use of a block. From Spike’s Tactical, I installed a Battle Trigger (NiB) with JP Rifles 3.5T spring set, ST-T2 (buffer) and ST-9BS (buffer spacer). The trigger was held in by KNS Precision anti-rotation pins. From Magpul, I added their ASAP (brand new at the time), MOE furniture in Foliage (hot at the time) and eventually a SSG which was a bitch to fit. Last, I sighted in a Burris FastFire 2 (not pictured), mounted on a AR-F3, at 7 yards.

My friends had all laughed when I told them of my plans for this project but after shooting it for the first time, they were all singing a different tune. This carbine was well balanced, lightweight and accurate within close range. It was low recoiling so follow up shots were easy. And, it was much quieter than their AR’s. This gun was reliable, never making so much as a hiccup. The only issue I had was with the magazines. 10 round Colt mags were hard to come by, California remember(?), so options were limited. I bought 4 ASC mags from 9mmAR.com because they were reasonably priced. The problem with these mags was that they were too small, barely protruding from the magwell which didn’t leave much room for clearance and like most 10 round mags, would only fit 9.

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