The AR family of rifle platforms is among some of the most popular ever created. The AR-15 is widely favored due to its modularity, making it adaptable to fit different scenarios. For added power, its bigger brother, the AR-10, offers similar customizability and can chamber larger calibers like .308 and 6.5 Creedmoor.
While both the AR-15 and AR-10 are highly popular rifle options, another AR platform, the AR-9, has carved out its niche. The AR-9 is a unique pistol caliber carbine based on the iconic AR-15. Sharing many of the same benefits, it’s become a popular option for home-defense, competitions, and recreation.
Although it’s similar to other AR variants, the AR-9 has multiple unique features that set it apart from the rest.
What is an AR-9
An AR-9 is a 9mm pistol caliber carbine based on the AR-platform. In recent years, they’ve become increasingly popular. The modern AR-9 is based on the Colt Model 635, better known as the Colt 9mm SMG, which was introduced in the early 1980s. Essentially, it was a 9mm version of the M16 that used a closed bolt direct blowback system instead of the M16’s direct impingement gas system. Aside from these key differences, the two platforms shared the same receivers, furniture, and controls.
One of the core design choices that led to the Colt SMG’s success was its use of a closed bolt system. Other 9mm sub-guns at the time most often used an open-bolt system, which, while effective, were comparatively difficult to control since they had much more inertial mass from their bolts.
AR-9s Today
Today most of the commercially available AR-9 models use the same closed bolt and direct blowback gas system as the original Colt 9mm SMG, offering a simplistic operating system and low recoil thanks to their use of the 9mm cartridge. This has cemented the AR-9’s reputation as a reliable pistol caliber carbine, making it one of the most popular PCCs on the market.
AR-9 firearms are available in an assortment of configurations, with the most popular ones being pistol and SBR configurations. Since 9mm doesn’t need a long barrel to reach its optimal velocity, AR-9s perform considerably well with shorter barrels. As such, it’s generally more common to see AR-9 pistols and SBRs as opposed to rifles. This isn’t to say that rifle length AR-9s are a bad choice, they just aren’t as common comparatively.
AR-9 Build Components
Like the AR-15, you can build an AR-9 from parts, and many of the components that make up the AR-9 are interchangeable with AR-15 components. However, there are some fundamental differences to consider. Below is an overview of some of the core components of the AR-9:
AR-9 Upper Components.
Upper Receiver: The AR-9 upper receiver plays a key role, dictating much of the firearm’s overall functionality. It uses the same mil-spec upper used in AR-15 builds, so building one is largely the same, with parts like the handguard, barrel nut, and charging handle all being the same for both platforms.
You can either build an upper from parts, or you can buy a complete one built by a manufacturer. Either choice is a solid way to go, but if you’re planning to build one, do keep in mind that doing so can come with a steep learning curve if you aren’t already familiar with the process. Our guide on assembling an AR-15 upper is a great resource to help you get started.
Barrels: AR-9 barrels share similarities to AR-15 barrels, using similar contours and shapes. However, AR-9 barrels lack a gas port since they use a direct blowback system, eliminating the need for a gas block and tube. When building your upper, there isn’t a need to choose a gas block, unless you’re building a clone of the original Colt SMG. Also, these barrels come threaded for muzzle devices but their thread pitch can vary depending on the manufacturer. Most commonly, AR-9 barrels feature a ½-36 thread pitch.
BCG: The AR-9 bolt carrier group is different compared to the standard AR-15 BCG. Designed for the direct blowback system, it uses a single-piece construction rather than multiple parts, since there isn’t a need for a locking and rotating bolt. Although most AR-9 BCGs use a similar one-piece design, there are different variants available that come with their own distinct advantages.
A popular AR-9 BCG is the radial delay blowback BCG, or RDB system, from CMMG. It uses a set of radially cut bolt lugs to create a mechanical delay to ensure a safer and more reliable operation. The chamber pressure forces these lugs to rotate and unlock before the bolt can move rearward, counteracting a lot of the felt recoil that comes with direct blowback gas systems. While effective, this BCG comes with the caveat of only being compatible with RDB barrels from CMMG, but both parts are commonly bundled and sold together in one package.
Lower Components
Lower Receiver: AR-9 lower receivers evolved significantly. Early AR-9 iterations used a magazine adapter fitted in a mil-spec AR-15 lower, but modern AR-9 lowers are designed to take specific magazines patterns.
GLOCK-compatible magazines are the most common ones used in modern AR-9 models as they’re widely available, with a plethora of extended 30- and 33-round extended options available too, which also makes AR-9s and 9mm GLOCK pistols a great pistol and rifle combo. In addition to GLOCK pattern lowers, Colt pattern lowers are still incredibly popular. These lowers use the original Colt SMG pattern magazines, which aren’t as readily available as GLOCK-compatible mags, but surplus magazines and modern reproductions from manufacturers like Duramag are easy to find.
Many of the core components, such as the trigger group, safety selector, grip, buffer tube, and other internal components, are the same as AR-15s. However, the buffer weight itself may need to be replaced to run in an AR-9, but many manufacturers produce dedicated AR-9 buffer kits to eliminate some of the guesswork in finding the right one.
Much like with assembling an upper, building out an AR-9 lower is essentially the same as building one for an AR-15. If this is unfamiliar territory for you, we recommend checking our step-by-step guide on assembling a lower receiver before you get too in the weeds on your project.
Factors to Consider Before Building an AR-9
Intended Use
Before you set off building an AR-9, there are some factors that need to be considered, the greatest of which being your intended use. Enthusiasts often build AR-9s for either home-defense, training/recreation, or competitive use. For home defense, a build with a shorter overall length (OAL) is often preferred as they’re better for maneuverability. For competitive use, your rifle’s barrel and overall length of your rifle is dependent on the restrictions put in place by your competition league. Lastly, for recreational/personal projects, you can realistically opt for whatever best fits your preferences. Just remember that all NFA rules and regulations, and all state laws, apply regarding barrel length and OAL.
Magazines
We mentioned previously that AR-9s can use either GLOCK or Colt pattern 9mm magazines. To briefly recap that section, GLOCK-compatible magazines are by far the more common magazine type between the two. If you’re looking to keep your magazine diversity to a minimum, or just want to have an option that’s a little more readily available, GLOCK-compatible magazines are the way to go. Still, Colt magazines are a practical choice, but keep in mind that their availability isn’t on par with GLOCK-compatible magazines.
An added point of consideration is the material of the magazines. Colt pattern magazines are most often made of stainless steel, though there are polymer options available too. In contrast, GLOCK pattern magazines are almost entirely made of polymer across all the manufacturers creating them. It goes without saying that steel is much more durable than polymer. So, if you’re planning to run your AR-9 in inordinately rough conditions, you might find benefits in Colt pattern magazines.
Accessories
If you plan to add accessories and other parts to your AR-9, it’s crucial to ensure it can adequately support them. Regardless of whether you’re wanting to add foregrips, sling mounts, or weapon lights to your AR-9, they’ll all require you to have a free-floating handguard. Fortunately, it’s common for AR-9s to come pre-equipped with free-floating handguards from the factory, making the process of accessorizing your firearm an easy one.
Conclusion
The AR-9 is easily one of the most popular PCCs on the market, blending the low cost and recoil of 9mm along with the adaptability of the AR-15, making an excellent choice for a wide array of applications.
As you venture into building your own AR-9, it’s crucial that you remember to take your own needs and preferences into consideration. Like the AR-15 or AR-10, AR-9s can be tailored to fit distinct roles. So, when you begin planning your AR-9 build, it’s paramount that you research all your options to ensure your final product aligns with your current goals.
With your AR-9 build complete, you’ll be ready to start kitting out to better fit your needs. Our guide on quick and easy AR upgrades goes over a lot of simple yet effective upgrades you can make on your AR-9.
