Best AR-15 9mm Conversion Kits

The AR-15 is the most popular rifle pattern in the United States that hundreds of companies manufacture, either in whole or in part. While the standard caliber .223 Remington/5.56mm is accurate, powerful, and light recoiling, many gun owners select pistol-caliber variants or convert existing rifles to handgun cartridges, such as 9mm Luger, .40 S&W, and .45 ACP. There are multiple reasons for this, from reducing training costs to pairing your rifle with your sidearm.

Best AR-15 9mm Conversion Kits

• Faxon Firearms Gen 2 9mm PCC Bolt Carrier Group Complete
• Foxtrot Mike Products PA Exclusive FM9 3 Gun 9mm Complete Upper
• Stern Defense AR-15 Conversion Block
• Hahn Precision Conversion Block
• Angstadt Arms AR-15 9mm Barrel

Converting a .223/5.56mm AR-15-pattern rifle to 9mm requires either a dedicated upper receiver — complete with 9mm barrel, bolt carrier group and buffer spring assembly — or the installation of these individual parts into an existing upper.

The standard AR-15 rifle uses a direct-impingement gas system and a bolt-carrier group to match. In 9mm, as with many semi-automatic pistol-caliber carbines and submachine guns, the operating system is simple blowback.

Assuming you already have the 9mm upper receiver or the necessary component parts, you must install an adapter to continue using your existing lower receiver with 9mm handgun magazines.

1. Faxon Firearms Gen 2 9mm PCC Bolt Carrier Group Complete

If you’re interested in altering your existing upper receiver to accommodate a different caliber, one of the first groups or assemblies you must change after the barrel is the bolt carrier group. A .223/5.56mm BCG uses a rotating bolt with 7 radial locking lugs that engage corresponding recesses in the barrel extension. A direct-impingement or short-stroke gas-piston system actuates it.

However, most 9mm pistol-caliber carbines and submachine guns use a blowback system, where the mass of the bolt and the tension of the recoil spring oppose the breech’s opening. Faxon Firearms Gen 2 9mm PCC Bolt Carrier Group is one of the simplest purchases toward converting your rifle to a pistol caliber.

Faxon machines this bolt carrier group from 8620 alloy steel, and it’s on the heavy side, coming in at 14.9 oz.

Its use as a blowback alternative can still accommodate a traditional AR-15/M16 extractor and dust cover. The ramped bottom is also compatible with standard mil-spec fire-control groups.

2. Foxtrot Mike Products PA Exclusive FM9 3 Gun 9mm Complete Upper

If you’d rather replace the upper receiver entirely, Foxtrot Mike Products offers you that option. The FM9 3 Gun 9mm Complete Upper features a 16” 9mm barrel with a 1:10” rifling twist rate housed in a 15” M-LOK handguard. This twist rate stabilizes a wide variety of 9mm bullet weights.

Foxtrot uses a proprietary locking system to ensure the monolithic upper receiver and handguard remain firmly attached at all times. If you’re left-handed, you can appreciate the ambidextrous charging handle, which features oversized latches, so you’ll never have difficulty loading or unloading the weapon.

Although the 9mm cartridge produces soft recoil, the muzzle has a Primary Weapons Systems compensator to reduce muzzle climb from rapid-fire shooting sessions. This is perfect for fast-paced competition where speed and accuracy need to be balanced.

Because this is a complete upper, it also includes a 9mm bolt carrier group designed for blowback operation.

3. Stern Defense AR-15 Conversion Block

Once you have a suitable upper receiver, look for conversion blocks or adapters that enable you to use your existing lower receiver. The magazine well for a USGI 5.56mm magazine is considerably longer than that of a double-column 9mm pistol or submachine gun magazine. You can use 9mm or .40 Smith & Wesson handgun magazines, such as those of the popular Glock series, by installing a conversion block.

Stern Defense’s Magazine Conversion Block is easy to install — requiring no special tools — and can lock the bolt open when the last round is fired, allowing for rapid reloads using the bolt catch.

The company manufactures its magazine adapter using 6061-T6 aluminum alloy to reduce weight, but the feed ramp is NiB 4140 alloy steel. This conversion block is compatible with bolts cut for Glock magazines.

4. Hahn Precision Conversion Block

For use with Colt and UZI 9mm magazines, as opposed to those used with Glock firearms, this conversion block lets you convert your AR-15 to a pistol-caliber carbine akin to that of a submachine gun.

Hahn uses the standard AR-15/M16 bolt catch because of its superior durability. Installation is simple and requires removing the existing bolt catch, insertion of the adapter, and re-installation of the bolt catch. This conversion block also features a bolt hold-open function, so when you fire the last round, the bolt locks open.

The company machines the block from an aluminum billet, so it’s highly durable.

5. Angstadt Arms AR-15 9mm Barrel

One of the essential parts of a caliber conversion is the barrel. If you don’t think you need a full-length rifle barrel to take full advantage of the 9mm round, you may opt for a more compact option. This is also perfect for AR-15-pattern pistols with stabilizing braces and short-barreled rifles.

The Angstadt Arms lightweight-profile AR-15 9mm Barrel is 4.5”, which is roughly equivalent to the Glock 17 service pistol, and features a 1:10” twist rate, like that of the Foxtrot Mike Product’s upper. Angstadt manufactures its barrels using 4150 chrome-moly vanadium steel and applies a Melonite finish for improved corrosion and wear resistance. At this length, you can build a compact 9mm carbine for home defense to maneuver effectively in confined spaces, such as hallways and door frames.

Pistol-Caliber Carbines

There are advantages to using an intermediate- or full-power rifle cartridge if you possess a shoulder weapon for self-defense or hunting. These include:

• Accuracy and range: A high-velocity cartridge using a more aerodynamically efficient projectile design allows for a flatter trajectory and less wind deflection. It is also less affected by air resistance (drag). While the effective range of a handgun is usually measured in tens of meters (e.g., 25–75), it’s often measured in hundreds for rifle ammunition (e.g., 300–500).
• Power: Many dedicated rifle cartridges inflict more traumatic wounds due to increased kinetic energy, yaw, tumbling, and fragmentation. These terminal-ballistics phenomena are more common to high-velocity rifle bullets than low-velocity handgun ammunition.
• Penetration: For hunting, barrier penetration, and penetrating body armor in defensive or tactical scenarios, the rifle cartridge offers increased penetrating power. This can also increase the risk of injuring or killing bystanders, requiring you to carefully manage your ammunition selection and environment.

However, when firing handgun ammunition in a shoulder-fired weapon with a carbine-length barrel, you can take full advantage of the round’s capabilities. There are several reasons to choose a pistol-caliber carbine. These are:

• Ammunition commonality: One of the most common reasons to carry or own a rifle chambered in a handgun cartridge is ammunition commonality with your sidearm. This was standard practice in the Old West — your Winchester lever-action rifle and your Colt Single Action Army both fired the .44-40 or .38-40 cartridge. If you typically carry a 9mm Glock, a 9mm carbine allows you to draw from the same ammunition pool for both weapons, often using the same magazines.
• Recoil: Whether you’re comparing a 9mm carbine to a .223-caliber rifle or a 9mm handgun, the 9mm round produces less recoil in a shoulder weapon.
• Muzzle blast: Firing a rifle cartridge indoors produces a loud and concussive blast, especially when using a short-barreled weapon. If you intend to use your carbine as a home-defense weapon, the 9mm cartridge generates far less noise and flash than a .223/5.56mm, .300 Blackout, or 6.5mm Grendel.
• Stability: Unlike a handgun, a rifle provides multiple points of contact between you and the weapon. This increases your control, allowing you to manage recoil and muzzle climb, keeping your shots on target. While this is useful for competitive shooting, it’s also critical for self-defense.
• Power: Although 9mm carbines come in various barrel lengths, those replicating standard-length rifles allow you to squeeze more velocity out of the 9mm cartridge, increasing its range and effectiveness. While this still isn’t comparable to a 5.56mm or .300 Blackout, it boosts the ammunition performance when fired from a handgun.
• Accuracy: Aside from the longer barrel, the sight radius — the distance between the front and rear iron sights — also increases when using a carbine or rifle. This improves the precision of your sight picture.
• Accessories: If you opt for a rifle with an M-LOK or quad-rail handguard, you have several points for attaching accessories, such as weapon lights and sighting systems. A light can be a lifesaver when using a rifle for home defense.

In Conclusion

Converting your .223/5.56mm AR-15 to 9mm has several advantages, such as ammunition commonality with your sidearm, reduced muzzle blast, and low-cost plinking. It also has its downsides, such as reduced effective range and power. However, if you’ve determined that the pros outweigh the cons, there are several parts and assemblies that you can buy—these range from bolt-carrier groups and magazine adapters to complete uppers.