The Evolution of the 9mm AR Carbine

The Evolution of the 9mm AR Carbine

The Evolution of the 9mm AR Carbine
Christopher R. Bartocci
Features, History, Volume 7, V7N6

ABOVE: The Colt 9mm-pattern carbines never achieved the success they should have. They were never really pushed by Colt sales due to Colt not wanting anything to compete with their own M4 carbines. However, this is an excellent 9mm weapon system. Shown with SWAT Officer Mike Magri, this modernized 9mm SMG has all the versatility of its 5.56mm big brother.

Although the 9mm carbine/SMG is rarely found in U.S. law enforcement, it is still found throughout the world: the Caribbean, India, Central and South America, to name a few. In the early 1980s, Colt decided to get into the 9mm business. At the time, the majority of the 9mm SMG business was owned by Heckler & Koch with their MP5. Colt put one of the finest engineers in the industry, Mr. Henry “Hank” Tatro, on the project. His product development spawned some very interesting prototypes. Hank had to work around an important requirement: to keep as many parts in common with the M16 as possible. The first model was actually an open bolt operated SMG. The bolt was one piece with a slightly modified extractor. The barrel was cut down to around 10 inches. There was a two-piece magazine well adapter, which permitted the use of a slightly modified UZI magazine. The ejector was mounted into the rear adapter and a feed ramp was attached to the forward adapter in the magazine well. One of the more interesting features is that the SMG had a grip safety, similar to that of the UZI as well. Initial testing showed two things. First, that Hank needed to completely rework the extractor and second, the open bolt mechanism he had was not reliable. Even with the grip safety, if the SMG was dropped it was prone to release the bolt and unintentionally fire a round or two.

So the decision was made to go with a closed bolt mechanism. The operating dynamics of a 9mm are quite different from that of the 5.56mm cartridge. The faster burning pistol powder causes a higher cyclic rate and needs to be slowed down. The closed bolt mechanism chosen is a blowback operation. Once the trigger is pulled and strikes the firing pin, the mass of the bolt, action spring and hammer spring provide enough resistance to keep the breech closed until pressures drop enough to safely extract and eject the fired cartridge case. The buffer is made out of steel and is comprised of two pieces with three rubber disks in between them. This not only provides the proper amount of mass, but also prevents bolt carrier bounce on fully-automatic fire. When firing, early rifles showed that un-burnt powder would strike the shooter in the face and it would sometimes burn the shooter. To correct this, Tatro designed a gas deflector to be added to the rear of the ejection port. Many misconstrued this for a fired cartridge case deflector. Due to the ejection mechanism, left-handed shooters would not be struck by fired cartridge cases. The ejection port dust cover was cut in half so the gas deflector would fit.

This is a early model of the Colt 9mm SMG. Notice the lack of threads on the muzzle but, more importantly, the grip safety on the back of the pistol grip. This early Colt Gun Room model fired from the open-bolt mechanism.

The bolt was redesigned. There is a large steel weight pinned to the rear. The extractor has more resemblance to that of a M1911 but it is designed to snap over the rim rather than having the rim slide under it as with the M1911. The firing pin is shortened and has a spring. Due to pistol ammunition having softer primers, the spring is needed to prevent slam fire conditions. The ejector is fixed to the magazine well block and slides along a track in the bolt. Due to stacking of tolerances, the ejector normally has to be adjusted so it sits along the track. If it is not bent inward properly, the ejector could miss the rifle altogether, causing a failure to eject. Both selective fire as well as fully automatic versions of the carrier were made.

The lower receiver is a standard M16/AR-15 lower receiver. Another modification made to the trigger mechanism was the use of stainless steel trigger pins. Due to the high bolt velocity, the hammer would get “slapped” down quite hard and break the standard hammer pin. The standard 2-poition receiver extension was used with the mentioned 9mm buffers. Also introduced was a cost effective 1-piece buffer for use in semi-auto-only carbines.

The early magazines were UZI 32 round magazines with a mag catch slot cut for the AR mag catch. Later Colt went on to develop its own magazines, manufactured by Metalform. For a short period of time Colt used magazines manufactured by C Products, but later switched back to Metalform. Colt sold both 20- and 32-round magazines.

The first open-bolt prototype used a modified M16 extractor. This proved problematic and was quickly abandoned (so was the open bolt mechanism in favor of a closed bolt blowback operation). Notice the stamp on the magazine well, “Colt Gun Room,” indicating it was a prototype.

The first model offered was the R0635 9mm SMG. This would go on to be the standard one sold via law enforcement and export sales. This flagship is a selective fire, 10.5-inch chrome-plated barrel with the fixed carrying handle (adjustable for windage only). The barrel has a birdcage (A1-style) flash suppressor and fixed front sight base. Standard single heat-shield handguards were used as well. Other models basically differed in fire control groups.

Colt went on to introduce the commercial 16-inch AR-15 9mm carbine (R6540), which was for the most part identical to the R0635 with a few changes. The upper and lower were the commercial large diameter front pivot pin, which used a screw and collet. The bolt was a semi-auto-only version. Next to market was the Pre-Sporter rifle that was updated with a lower made from an A2 forging. Added to this rifle was the magazine BOSS. There was a transition from the screw and collet to the MIL-SPEC pin with a screw on the left side to the use of a captive pivot pin. It was around this time when Colt switched to the 1-piece mag well adapter. First versions were secured by way of a tensioning screw. This did not work out well because, when overtightened, the magazine well would be flared and ruined. The final design was the 1-piece mag well adapter drilled and pinned into the receiver. Then came the Colt Sporter 9mm, which Colt voluntarily modified. The bayonet lug was removed and the telescopic stock was replaced with a fixed stock. The fire control group was modified to use 0.170-inch large pin hammer/trigger pins instead of the standard 0.154-inch pins, then an automatic sear block was machined into and pressed into the lower receiver. Then came the Assault Weapons Ban of 1994. To comply with the law, Colt removed the flash suppressor and hence created the Match Target 9mm Carbine (MT6430).

After the sunset of the ban in 2004, the AR6450 was sold to the commercial market. In late 2008, a change was made to go back to standard 0.154-inch hammer and trigger pins. The AR6450 no longer had the restricted marking. Colt released a new model, the AR6451. The difference was the use of a flattop upper receiver. Colt usually has one run a year of the 9mm.

Close-up views of the prototype receiver. Notice a standard M16 lower with the mag well adapter pinned in. This photo shows a close up of the grip safety as well.

The Updated 9mm SMG/Carbine

Like its 5.56mm big brother, the 9mm carbine has been taken on by numerous companies. These companies have dedicated large sums of money to enhancing the carbine design, not only in the areas of reliability, but in making it just as modular as the M4. You can now basically configure the 9mm in the same way you can the M4. This includes the use of rail systems, enhanced fire control groups, stocks, pistol grips, buffers and backup sights. Any of the modern military grade optics can be used on it as well. For this article, this author built a modern 9mm carbine out of hand-selected components which he felt were a massive improvement over the standard legacy 9mm carbine. As a disclaimer, this is like an Erector Set, there are endless things you can do and this is but one vision of the ideal 9mm carbine.

Perhaps the most significant development in the 9mm AR (since it came to market by Colt) was designed by Jon Beaudry of Double Diamond Law Enforcement Supply. Jon designed and manufactured a dedicated 9mm lower receiver. Unlike all the ones before it, which were all based on the standard lower receiver and use a magazine well adapter or have the well cut to accept the 9mm magazine, such as the CMMG, the DDLE lower is manufactured from a billet which permits it to have the magazine well cut back to the proper size of the 9mm magazine. Not only does it look better, it is lighter because the design got rid of unused aluminum. Beaudry put a nice flare on the bottom of the well for low-level light reloading. The trigger guard is integral with the lower receiver. To deal with the ejection problems, Beaudry developed a free-floating ejector that aligns properly with the bolt to ensure against failures to eject. He improved on the bolt catch as well, there is more gripping surface to ensure positive bolt lock. DDLE offers the receiver in both 6061-T6 as well as 7075-T6 aluminum. There is also an adjustment screw to adjust the tightness of the upper and lower receiver. DDLE broke off with their partner in late 2014 and former partner Russ Klawunn opened up his own shop, Quarter Circle 10.

Shown is Colt’s production model 9mm SMG (R0635). This is the most commonly sold Mil/LE version of the Colt 9mm family of firearms. Notice the 10.5 inch barrel, standard carbine handguards and A1 carrying handle, as well as the gas deflector behind the ejection port.

On the lower receiver, a Magpul MIAD pistol grip was installed and a semi-automatic-only fire control group was installed using Colt stainless steel hammer and trigger pins. A Battle Arms Development, Inc. ambidextrous Safety Selector was used, as well as their Enhanced Pin Set. The Yankee Hill Machine (YHM-9758) carbine sling adapter was installed to allow a single point or standard sling use. The VLTOR 6-position Receiver Extension was used and the black modstock was selected. The Norgon Ambi-Catch (magazine catch) was used as well.

The upper receiver is a custom VLTOR MUR (Modular Upper Receiver) with a modified side plate. The fired cartridge case deflector was ground down and the gas deflector and ejection port cover were added. The barrel is manufactured by Yankee Hill Machine. It is a fluted barrel and attached to the end is a Vortex flash suppressor manufactured by Smith Enterprises, Inc.. The handguard chosen is manufactured by Centurion Arms, the C4 10-inch free floating rail (part number: 060910). It does not require any special barrel nut and provides quad MIL-STD-1913 rails. On the left, right and bottom rails are Manta advanced rail protectors. They are unmatched in heat (and even cold) protection.

The bolt is a standard selective fire Colt bolt. The charging handle is the VLTOR Gunfighter charging handle which has a high-profile extended latch, making for easier actuation. For folding backup sights, the A.R.M.S., Inc. #40L rear and #40L-F front sights were used. These are metal sights of the highest quality.

The Colt 9mm weapons are extremely reliable and durable. Shown is a mud test conducted by the Indian Special Forces. The SMG functioned flawlessly when fired.

There were several buffers tested in the enhanced 9mm carbine. The original legacy buffer is the same length as the standard 5.56mm. The problem is the bolt carrier group is about 0.450 inches longer on the standard 5.56mm rifle due to the bolt being separate from the carrier. That caused two problems. First, it gave 0.450 inches of acceleration before the bolt slammed into the bolt catch, causing the bolt catches to break. It also exposed the fire control group compartment, allowing a fired cartridge case to enter and cause a malfunction if the SMG experienced a failure to eject. Colt did not remedy this until around 2009 when they added a spacer to the rear of the buffer spring. Due to the heavy buffer, the recoil is much more stout that the 5.56mm rifle.

Blitzkrieg Components provided two of their buffers for testing. One is a hydraulic buffer, which has the proper overall length for the 9mm, so no spacers are needed. This buffer made a significant difference on perceived recoil. In fact, this buffer is left in the carbine after testing. Hydraulic buffers have been around for a while and the problem has always been their reliability. Like the 9mm carbine/SMG, they have also evolved. The other buffer tested was the Blitzkrieg Components 9mm AKTIVE Buffer. This is also the proper length and offers some cushion as well to reduce recoil, certainly several steps ahead of the standard buffer, but not quite as good as the hydraulic.

The magazines chosen were the time-tested Colt Metalform 20- and 32-round magazines, as well as 20- and 32-round magazines by Ammunition Storage Components. The Metalform magazines use a metal follower and the ASC magazines use a bright orange follower made of polymer. All of these magazines have witness holes to see how many rounds are in them.

The Colt 9mm SMG, shown doing a water test by the Indian Special Forces (Octopus).

The optic chosen is the Trijicon Reflex sight (RX34A-51). This has a wider screen (42mm) compared to the SOPMOD (24mm) optic. There is a honeycomb diffuser to prevent glare off the lens from giving away the shooter’s position. Due to the larger screen, the optic has a mount surface to optical axis of 1.506 inches. This does not allow for co-witnessing with iron sights. The sight has a 4.5 MOA Dot (amber) which is powered by both a tritium lamp as well as fiber optics. The sight is used with both eyes open and weighs 8.2 ounces without the mount. Due to the limited range of the 9mm pistol cartridge, this would be an ideal option for an optic.

This rifle was tested with two different types of ammunition. First is Winchester 9x19mm NATO M882 ball. This is the standard U.S. government-issue ammunition with a 124gr full metal jacket, firing at 1,185 feet per second. This velocity would be considered a +P by SAAMI standards. The ammunition procured was from their Law Enforcement ammunition line (part number RA9124N). The second is manufactured by Black Hills Ammunition. No malfunctions encountered in nearly 1,000 rounds.

As previously stated, this is but one variation of the countless number of accessories that are out there. With the selected gear, anything you would want on a M4, you can place on the 9mm carbine. The 9mm carbine has come a long way since the initial design Hank Tatro did in the 1980s. The one great thing about the boom of manufacturers of this platform is that each company will try to improve upon the products to make them just that much better. In fact, they compete with each other to see who comes out with the better mousetrap.

Close-up view of the receivers (right side) of the Colt SMG (R0635). Notice the SMY has semi as well as full auto capability, this SMG has a 20-round Metalform 9mm magazine, A1 carrying handle and rear sight, as well as the gas deflector behind the ejection port.

The 9mm dedicated lower receiver (Jon Beaudry design) offers several enhancements over the Legacy design. Notice the actual feed ramps in front of the magazine (right) compared to the smooth ramp of the legacy (left). Also notice the Beaudry-designed free floating ejector (right) compared to the Legacy (left), which requires adjustment after assembly. Also notice the Beaudry design has a dedicated 9mm magazine well, not a converted M16/M4 magazine well with an adapter.

Around the same time as the build of the custom 9mm carbine was completed, a brand new magazine hit the market, manufactured by X Products. This is a rotary 50-round magazine that is quite durable and manufactured from aluminum. The bolt used in this 9mm carbine build is a Colt newer-generation enhanced bolt. The portion which picks the round up off of the magazine is smaller than the other ones, which are based on the earlier Colt 9mm bolts. There may be compatibility problems if you have this older-style bolt. Quarter Circle 10 is now offering a bolt which is compatible with the X Products drum and Glock magazines.

The Colt-pattern/UZI 9mm magazines are very difficult to load and will give you an extremely sore thumb. If you have one of these systems, the Maglula UpLULA for the Colt 9mm SMG mags is an absolute must.

One of the more significant advancements recently in the 9mm carbine arena is the hydraulic buffer. The recoil on the 9mm is more stout than that of the 5.56mm rifle due to the heavy mass of the 9mm bolt. Shown are two of the buffers tested (both manufactured by Blitzkrieg Components, LLC). The top is the hydraulic 9mm buffer, which is made longer to avoid bolt acceleration before the bolt impacts the bolt catch, keeping the trigger compartment covered to prevent cartridge cases from entering the trigger compartment. The bottom is the 9mm AKTIVE buffer (it’s not hydraulic, but it still cushions the blow of the 9mm bolt to the rear).