What is an AR-9?

The AR9 is an AR style lower receiver made specifically to shoot 9mm or .40 S&W Glock with Glock style magazines. It shares all the same furniture that an AR-15 does, and is compatible with many of the same parts as well.

Most people are familiar with the AR-15 and the AR-10 but some might not have ever heard of the baby brother to both - the AR9. The AR-9 operates off of the same mil-spec platform as the AR15 but is chambered in 9mm and oftentimes can break down into a pistol bag or backpack for easy concealment. Let’s take a look at the 9mm AR breakdown and see why the AR9 might be a great option for many uses!

PCC Background History

Pistol Caliber Carbines have been around since the 1800s and for good reason: the ability to share ammo between a sidearm and a longer, more controllable carbine rifle is a distinct advantage only a PCC can offer. From Winchester lever guns to Colt Single Action Army revolvers, we’ve traded up in modern times for AR-15s and Glocks. Naturally, the relationship between sidearm and PCC has also shifted to reflect this in the development of AR9 lower receivers.

The Pros of Building an AR9 Pistol

The main draws to AR9 pistol kits are their low recoil, excellent maneuverability, and shared ammo with a sidearm. AR9s are excellent truck guns due to how compact and light they are, making it the perfect choice to stuff behind or under a seat. Generally, an Ar9 pistol upper is going to be under 16”, so making space for one in any car won’t be particularly difficult.

An Ar9 pistol kit is also a great option for range trips: Most shooters that just want to slap steel targets don’t want to spend their entire paycheck restocking all of their rifle ammo after a range day, so pistol ammunition is a good middle ground solution. Even now, with lingering pandemic pricing, it’s possible to purchase twice the amount of steel case 9mm Wolf than steel case Tula .223. Not to mention, Glock owners wouldn’t even need to bring spare mags. Cheaper ammo, less mags to buy and bring, what’s not to love?

The weight of the gun is relative to the small size of the caliber which also adds to the AR9’s appeal: AR9 pistol kits are going to be much more controllable for someone who doesn’t shoot often or at all. It makes sense to hand over a 9mm carbine to a newbie so they can get used to the same ergonomics of an AR-15 without the larger recoil of a rifle round. We actually have a whole blog post further explaining the advantages the AR9 has over the AR-15 if you’d like to learn more about that.

AR-9 for Home Defense

The AR15 is no doubt an excellent choice for home defense but would an AR9 be a better option for some? Some people might not be able to comfortably carry the weight of an AR-15 so the AR9 is an excellent choice due to its lightweight and 9mm round being known as an excellent defensive caliber - especially when utilizing hollow point rounds. Hollow points are a great choice for self defense because the round is less likely to pass through a target or wall and hit something beyond it. Full Metal Jacket (FMJ) rounds will have a high chance of passing through multiple barriers like soft targets and drywall very easily; making them far less preferred for home defense.

To avoid getting trouble with the ATF and NFA rules, you can build your AR9 to have a shorter barrel and attach a pistol brace to give your more firing stability and legal prowess. The shorter overall length of your pistol caliber carbine allows for better weapon manipulations around tight corners and narrow hallways a home may have. Let’s have a look at some more advantages an AR-9 Build can provide for your home defense.

AR-9 for Home Defense Advantages

AR9 Pistols are an excellent choice for home defense. Being small and maneuverable is key when it comes to home defense and as stated above - it is hard to beat a 9mm hollowpoint for a home defense caliber. As stated above - 9mm makes an AR9 pistol an incredibly good option for home defense. Some pros for the AR9 pistol as a home defense weapon:

• Dynamite comes in a small package
• 9mm excellent for close range work
• Maneuverable
• Ability to attach accessories - red dot sights, weapon light, etc.
• Extremely reliable
• Easy to store and quick to deploy in an emergency 

Is an AR9 Pistol Any Different From an AR-15?

Although the AR-15 and the AR9 share a good chunk of parts and aesthetics, they are far from being the same gun. The most notable difference, mechanically, would be the gas system: AR-15s operate through a Direct Impingement gas system, which takes the gas from the explosion of the cartridge and redirects it into the gas tube, which forces the gas to push onto the gas key of the bolt carrier group and pushes it back.

AR9s on the other hand use straight blow back, which is when the bolt is directly pushed back from the force of the gas inside the chamber. Our AR9 pistol kits also come with their own proprietary ejector that is fixed into the lower receiver to account for the wider diameter of the 9mm casing. However, it is possible to attach an AR9 upper to an AR-15 lower and then convert the mag well to accept Glock magazines or purchase AR-15 magazines converted to accept 9mm cartridges.

Building An AR9 Pistol Kit

Building an AR9 really isn’t all that different from building an AR-15 and can be very rewarding, not to mention a ton of fun! If you’re building one completely from scratch, the milling process with an 80 lower receiver is 100% the same. No need to buy specialized tooling for a 9mm pistol or get a special 9mm Jig. If you’re working with an 80 lower, it’s as straightforward as it’s 5.56 NATO brother. Here’s our best advise on what you should be looking for:

Barrel Length

Unlike an AR-15, the barrel length doesn’t matter a whole lot when it comes to performance. You could have an extremely short barrel and the recoil still won’t be a big deal. It’s more likely that you’ll choose a barrel based on other factors such as whether you plan on running a suppressor or running subsonic ammunition.

If a projectile is traveling faster than 1,125 fps, then it is going to break the sound barrier creating that loud ‘crack’ you’ve heard practically every time you’ve been shooting.Bullets that break the sound-barrier are supersonic. Bullets traveling less than 1,125 feet per second, then it’s considered ‘ subsonic ammunition’. These bullets will not break the sound barrier, and will be significantly more quiet when using a suppressor. However, longer barrels will give the gas from the gun-powder igniting more time to push the bullet forward in one direction which would increase velocity. So if you’re planning on using sub-loads, a shorter barrel might be better.

Barrel length does affect the gassing of any AR9 pistol upper. A longer barrel equals a less violent gas system and a shorter barrel will increase the perceived felt recoil of the weapon. This concept remains true for basically any firearm, however, it’s kind of irrelevant when it comes to the AR9. With a decent muzzle device like a compensator and a standard pistol buffer setup, the recoil you experience is honestly comparable to an airsoft gun.

Colt Or Glock Compatibility?

AR9 pistol lowers have two standard configurations, which are the Glock magazine fed lowers and the Colt 9mm magazine lowers. Although both work great,the vast majority of AR9 complete pistol lowers are made for Glock due to how popular the handgun is. Glock also has a much wider variety of magazines that also have huge aftermarket support. That being said, if you’re going for the Colt 9mm AR aesthetic no one is going to hold that against you. Well, except maybe Glock guys.

It should be noted that trying to mix Colt AR9 parts and Glock AR9 parts tends to cause more problems than it’s worth. Stick to one brand and design to keep plinking with your new gun with fewer issues, if any at all.

Upper Receivers and LRBHO

One of the most desired features in an AR9 pistol upper would be the Last Round Bolt Hold Open (or just LRBHO for short). With most AR9 builds, this will only work if the upper itself is capable of utilizing one. Some notable examples of AR9 complete upper receivers and stripped receivers with a LRBHO are Aero Precision’s EPC-9 Upper, and the CMMG Banshee Upper. A LRBHO is not practical on the lower receiver because the space between the magazine and the bolt is shifted too far forward for a typical AR-15 bolt catch but some companies do manage to pull it off. This is why most manufacturers build it into the upper instead.

Similar to AR-15s, side charging AR9 complete uppers also exist: Moriarti Armaments offers a side charging upper for around $500. It also comes with a LRBHO to boot! Foxtrot Mike also offers side charging AR9 complete uppers for slightly less, although you will have to purchase one of their lowers to have a LRBHO.

AR9 Lower Parts Kit and Triggers

The AR9 lower parts kit and triggers are exactly the same as the ones used in AR-15swith the only exception being the ejector. For a quality AR9 trigger, look no further than CMC, a Texas-based company that makes the best bang for your buck 3.5 lbs single stage trigger. They carry both curved and flat triggers. For the lower parts kit itself, CMMG has an excellent Builder’s Kit for AR-15s that will work perfectly with any AR9 complete lower pistol receiver. CMMG also offers a complete lower parts kit with their own mil-spec trigger and A2 pistol grip if you aren’t quite looking for a higher end trigger just yet. For whatever reason… Although not ideal, you could cannibalize your AR-15’s parts and swap between the two if absolutely necessary.

AR9 Ammunition

If your AR9 build is truly just going to be a range toy or a solely-for-pleasure build, there’s no shame in using rounds with steel casings. Steel rounds have finally sunk to around 30 cents a round in some small corners of the internet, despite the recent Russian ammo ban. Brass prices have also gotten better if you aren’t looking for fancy 9mm loads.

For more defense oriented loads, consider the Grind Hard 90GR Extreme Defense 9mm, which offers impressive ballistics. Due to it being a solid copper projectile, it retains the same dimensions as a normal plated, lead cast bullet but will fly much faster. Copper bullets also don’t lose a lot of mass when they hit hard or soft targets and are less likely to break apart upon impact unlike lead core bullets. At a little over $1 a round, it certainly isn’t cheap, however most boxes of hollow point rounds (i.e. Hornady Critical Defense, Federal HST or Winchester Silvertips) will all cost about the same price range.

What Does an AR-9 Cost?

As with every AR platform pistol or rifle, prices can vary greatly in price. Expect to spend $800 at a minimum for a good AR9 pistol from a reputable company all the way up to $1500 once you factor in your optics. So pretty affordable and cheaper than an AR-15!

Why Not Just Convert An AR-15 to Shoot 9mm?

You could, but it’s usually not worth it: Things like the STERN Defense AR-15 to 9mm Adapter cost more than an 80 percent AR9 lower receiver alone. For around 20 to 30 more dollars you could just buy an 80 lower, lower parts kit and have a new gun ready to be built out. To convert an AR-15 to 9mm you would still need a 9mm upper and uppers can be the majority of the cost when building a gun. Less parts to mess with equals less failure points.

There is another option if you’re dead-set on keeping your AR-15 lower to run 9mm, and that’s the MEAN Arms EndoMag 9mm. It is offered as a conversion for Gen 2 and Gen 3 5.56 or .223 PMAGs and features a built-in ejector in each magazine. This is a great alternative to the STERN, as you don’t need to spend almost $200 dollars to keep the same lower. All you need are some PMAGs to be converted and you’re golden. The only caveat to these mags is the built in ejector, meaning you have to leave the magazine in to clear a round. If that doesn’t bother you, then it’s a fair product to consider.

Build an AR9 With Modulus Arms!

Building an AR9 build kit allows the shooter to customize every single detail of their perfect rifle! When selecting an AR9 build kit it saves a lot of time of having to choose each individual tiny part. Questions such as “What charging handle for an AR?” become a thing of the past. Simply select a kit with the main features we’ll be needing and then assemble. It couldn’t be easier and we might even end up saving some money as opposed to buying an off-the-shelf AR9 pistol or rifle that we’ll end up wanting to customize anyway.

Still need pointers on how to build an AR9 pistol? Not a problem! Check out our other blog posts for all things on 80 percent lowers. We also offer plenty of parts and tooling to get you started on milling out any other 80 lower you might want for a different AR build while using the Router Jig Extreme.