There Are Some Notable Differences Across AR Rifle Platforms
The AR-15 and AR-10 have multiple variants that bring additional versatility while keeping similar controls. But some variants like the AR-9 are significantly different from the base AR-15. We’re going to go over these differences so you know what to expect when building or purchasing an AR-9.
What is an AR-9?
An AR-9 is a pistol caliber version of the AR-15. This means it uses standard 9mm ammunition instead of 5.56 cartridges. While there are numerous differences, the AR-9 has some parts in common with the AR-15.
The upper receiver and trigger group are compatible between the AR-15 and the AR-9. However only some lower receivers are interchangeable, this is because some AR-9s are caliber conversions while others are dedicated 9mm guns.
Now let’s look at what makes them different.
Differences Between an AR-9 and an AR-15
The gas system is one of the major differences between an AR-15 and an AR-9. A standard AR-15 will either use a direct impingement gas system or a piston system in order to cycle the bolt. An AR-9 uses neither of these systems.
Instead, the AR-9 is a direct blowback firearm. This means you will have to use a different buffer spring and bolt carrier in order to have the firearm safely cycle. It also means that the AR-9 cannot use any of the standard gas tubes of AR-15 kits because no gas is being put back into the system.
The next major difference is the bolt carrier group. Since the AR-9 is a direct blowback system, the bolt carrier does not need to rotate. This means an AR-9 bolt does not feature any locking lugs, and is a single piece.
Since the bolt needs to be heavy enough to keep the chamber sealed during fire, AR-9 bolts tend to be relatively heavy. This can result in a more perceived recoil impulse despite 9 mm being lower pressure than 5.56 rounds. The actual recoil will be less than a 5.56 gun.
An AR-9 can use the same buffer tube as an AR-15, but you will need a heavier buffer spring to reliably push the bolt back into battery. Having too light a buffer spring will result in more failures to feed and similar malfunctions.
The AR-9 will also use a different barrel than an AR-15. AR-9 barrels are usually between 7 and 9 inches for best performance, however longer barrels are available. Which you choose will depend on the legal requirements of your area.
Using a 16 inch barrel will add some velocity to the round, however these added velocities can impact performance, especially in hollow point ammunition. Many hollow points are designed for specific barrel lengths in order to achieve proper expansion due to the velocity those barrels produce. If a round goes faster than it was intended to, the bullet may break apart too early or not expand.
You have three options for using an AR-9. One is with a bare tube while the other options are either with a stock or a brace. Depending on several court decisions, which one you use will be determined by whether or not the AR-9 fits the ATF requirements to be registered as a short-barreled rifle.
If you are using a 16 inch barrel, this should not be a problem and a stock will provide the most benefits when using an AR-9. However, be sure to stay up to date on the legal requirements of your area.
There are two options for an AR-9 lower receiver. One is a converted AR-15 lower with a magazine block that allows you to use pistol magazines. The other is a specialty lower than can only accept pistol magazines.
The first option allows you to use readily available AR-15 parts while the second option is less complicated. Availability will be the primary factor in selecting your lower.
Differences between the AR-9 and the AR-10/AR-308
The AR-10/AR-308 features even less interchangeability with the AR-9 than the AR-15 does. These are related primarily to the upper and lower receivers
The AR-10 upper receiver has several variations. This results in three different cut styles on the rear of the receiver. The earliest version which is found on original AR-10s and the SR-25 are shaped similarly to an AR-15. However there are two other styles, one developed by DPMS and the LR-308.
These changes to the rear of the receiver make the AR-10 upper incompatible with the AR-9 lower in addition to being larger than the upper of an AR-15.
Similar to its equivalent upper, the lower receiver of the AR-10/AR-308 is too large to accommodate the necessary internal parts of an AR-9. It will accept some AR-15 internals and buffer tubes, but AR-10/AR-308s are not as standardized as AR-15s. This means parts compatibility is an issue.
Why choose an AR-9?
With all these differences and the lower availability of parts, why should you choose the AR-9? There are three major reasons to use an AR-9 instead of an AR-15.
Using only one caliber of ammunition is easier to maintain than many different types. If you are invested in 9 mm but want a rifle sized firearm, the AR-9 will be a good option. That way you won’t have to purchase two different calibers.
Ammunition cost will also be lower than 5.56 in most cases which allows you to spend more time at the range while still being able to stock up.
More often than not, you will be using some form of Glock magazines with the AR-9. This means you use the same magazines for your pistol and AR-9, although you can use 9 mm magazines with varying capacities to fit your needs.
While the recoil might feel more aggressive due to the direct blowback system, AR-9’s are more controllable than an AR-15. This is because of the lower pressures that 9 mm puts out. If you struggle to control the recoil on an AR-15, the AR-9 will be very beneficial for you. Systems like the AR-9 are one of the reasons pistol caliber carbines are becoming more popular in the market.