Caliber - 9x19mm (9mm NATO)
Capacity - 20 or 32-round Colt-pattern mags; can also use modified UZI mags
Action - Blowback-operated semi-automatic
Barrel - 9.25" w/ integral 3-lug adapter
Weight - ~7 lbs.
In the mid-1980s, Colt released a 9mm submachine gun based on their M-16 rifle. The new SMG was blowback operated and featured a magazine well adapter to accommodate the 20- or 32-round double-column stick magazine. Despite these differences, the Colt SMG used many of the same components as the 5.56mm weapon and had a similar manual of arms. The SMG was quickly adopted by the DEA and several law enforcement agencies. Shortly thereafter, a semi-automatic-only carbine followed for the civilian market, with a 16" barrel and A2 or collapsible stock.
Though the 9mm carbine is no longer produced by Colt (except for small runs for Law Enforcement agencies), several companies offer Colt-pattern 9mm uppers and parts which work with standard .223 AR-15 style weapons. In addition to a 9mm upper and bolt group, one must install some kind of magwell adapter to accommodate Colt or modified UZI magazines. Theoretically, all the owner then needs to do is pop the .223 upper off the rifle, replace it with the 9mm assembly, install the magwell adapter and he/she is ready to shoot 9mm.
In the Beginning
Years ago, I purchased a Colt "Match Target" 9mm upper and a JRW Sports 2-piece magazine block with the intention of shooting 9mm in one of my AR-15s. After some experimentation, I decided to dedicate one of my Bushmaster lowers to 9mm use only by drilling and pinning the mag blocks in place. This made the blocks much more stable than with their original setscrew attachment, and eliminated the tendency to shift under rapid fire and with frequent magazine changes. The Colt upper ran well, but I wasn't particularly enamored with its fixed A1 carry handle and naked 16" pencil-thin barrel. I didn't have any choice at the time, as the only other maker of 9mm ARs was Olympic, and their products are not compatible with the Colt system or mag blocks. Then, Rock River Arms began to produce Colt-pattern 9mm uppers in several configurations, and the floodgates were opened. I sold the Colt upper to a Colt collector via the Internet, and gave the 9mm AR a mid-life upgrade using an RRA flat-top upper receiver and mid-length barrel assembly with a permanently attached Wilson muzzle brake (this was during the AWB years). But I still wasn't happy; my 9mm carbine was the same length and weight as my .223s, and bore little resemblance to the handy Colt SMG from which it was derived. Plus, I was anticipating being able to have the barrel threaded for a suppressor once the AWB expired, but screwing a can onto a 16" barrel would've made for a rather ungainly package. So I bit the bullet paid the $200 tax to register the lower receiver as a Short-Barreled Rifle, which would allow me to install a barrel assembly less than 16" long.
Short and Sweet
The gun's third configuration was completed after the demise of the Assault Weapons Ban in late 2004. It retained some of the components used previously, including the Bushmaster lower, RRA flat-top upper, First Samco pistol grip and ARMS #40 backup iron sight. But I switched the fixed A2 stock out for a Rock River M4-style 6-position adjustable (once again legal after the AWB sunset) and added a dedicated 9mm hammer and recoil buffer for smoother cycling and improved reliability. I also installed a SPOT MkIII "Aimpoint simulator" red-dot sight in order to have a similar sight picture to my M4 carbine. But the biggest change was up front. For the barrel, I selected a 9.25" custom piece from Mark McWillis at TROS USA. This semi-heavy profile barrel of excellent quality terminates in an integral HK-style 3-lug adapter, to which various types of muzzle devices can be quickly attached. Surrounding the barrel is a lightweight, free-floating rail system from Yankee Hill Machine. This provides mounting space for accessories (like vertical grips, sling mounts and white lights), improves cooling and promotes accuracy, while costing a fraction of the price of competing systems. The YHM tube extends to just behind the 3-lug adapter, meaning that a conventional front sight tower could not be utilized. Instead, I mounted a YHM flip-up front sight onto the tube's top rail. After assembly, the gun and tube were refinished in matte black Alumahyde II from Brownells. This spray-on, epoxy-based coating cures to a tough, attractive finish in just a few days at room temperature.
No gun is perfect, and the 9mm AR SBR is no exception. Felt recoil, especially with NATO-pressure or +P loads, is surprisingly stout. Fortunately, adding a slip-on recoil pad and shooting standard pressure factory ammo or handloads are easy ways to mitigate this. Next is the issue of reliability. While the gun has been MUCH better since pinning in the mag blocks and switching from converted Uzi to Colt factory mags, it's still not 100%. I believe this is due primarily to the design of the mags themselves; the 32rd Colt mags with the plastic followers have a tendency to "fountain" out the top if bumped. If this happens while inserted into the gun, a double- or multiple-feed will result. The older 20-round mags with metal followers seem to be better in this regard, as do the newer aftermarket "waffle" and stainless steel mags.
As a breed, 9mm ARs are cool and different. This little gun, however, plain kicks ass! The short barrel makes for a lightweight and maneuverable package, but doesn't suffer the drastic reduction in ballistic effectiveness that would be seen with a .223 of the same size. Plus, the gun's pistol caliber means I can use it at the local indoor range for some cheap AR trigger time when I don't have the time, ability or desire to get out to my "home" outdoor range. And then there's the "cool guy factor"... :-)
Update 10/11/08 The Yankee Hill lightweight rail system that had been on the gun for the past few years, finally came loose. The problem with the older YHM systems is that the railed fore-end threads onto a replacement barrel nut, and is only held in place by friction, via a "jam nut" that is tightened against the back of the tube (current versions have additional screws that lock the tube to the barrel nut). I used this as an excuse/opportunity to give the gun a bit of a facelift, and replaced the YHM system with the MCTAR-20 from Midwest Industries.
Update 4/3/08 My 9mm AR has remained more or less in the described configuration for a few years now, and has continued to provide yeoman service in Steel Challenge matches as well as in training and general range use.
Update 9/7/05 I competed in the July and August Steel Challenge matches at a local gun club, both times using the 9mm SBR to win the Carbine division! And the gun-grabbers say Black Rifles don't have a sporting purpose?!