9mm PCC Build
Building a 9mm AR Pistol Caliber Carbine
Caleb is back at the Brownells bench with a 9mm pistol caliber carbine project based on the AR-15 platform.
The lower receiver is already mostly assembled, so the primary focus of this project is the 9mm upper and the components that make a blowback AR-9 different from a conventional AR-15.
The finished build combines a Brownells lower and 9mm bolt carrier group with a Faxon barrel, Midwest Industries handguard, Dead Air suppressor, Aimpoint optic, and several Die Free Co. accessories.
Brownells AR-15 Lower Receiver
The foundation is a newer Brownells AR-15 lower receiver.
Caleb likes the relatively clean appearance of the receiver. The Brownells markings are kept minimal without a large logo dominating the side of the lower.
The receiver is already assembled for this video, allowing Caleb to focus primarily on the components needed to turn the standard AR-15 platform into a 9mm PCC.
9mm Buffer System
One important difference is the buffer system.
This build uses a carbine-length receiver extension with a 9mm-specific hydraulic buffer. Caleb explains that a blowback 9mm AR operates differently from a conventional gas-operated 5.56 AR-15, so buffer selection is an important consideration.
The hydraulic design also helps smooth out the recoil impulse of the blowback system.
Colt Magazines vs. 9mm Conversion Magazines
Caleb covers two approaches to feeding a 9mm upper from a standard AR-15 lower.
The first uses traditional Colt-pattern 9mm magazines with a magazine well adapter. Caleb chooses this approach for the build, in part because he likes the classic appearance of the straight Colt magazine.
The other option is a conversion-style magazine with external dimensions compatible with a standard AR-15 magazine well but internal geometry designed around 9mm ammunition.
Depending on the particular upper and magazine system, ejector configuration also needs to be considered.
ProMag Colt Magazine Adapter
For the Colt-pattern magazine setup, Caleb uses a ProMag adapter.
The adapter allows the standard AR-15 lower receiver to accept the narrower Colt-pattern 9mm magazine while retaining use of the AR-15 magazine release.
Once the adapter is in place, Caleb completes the lower receiver setup and checks the interaction between the magazine and bolt catch.
Last-Round Bolt Hold Open
Last-round bolt hold open is another consideration with a converted 9mm AR.
Caleb demonstrates that the Colt magazine setup can engage the bolt catch, but he also discusses how bolt travel and the particular buffer configuration can affect whether the system functions as desired.
There are multiple ways to configure a 9mm PCC, so the importance of last-round bolt hold open may influence component selection.
SBA5 Pistol Brace
This particular project is configured as an AR pistol rather than a rifle.
Caleb installs an SBA5 pistol brace on the carbine receiver extension before moving on to the upper.
As with any firearm configuration, owners should make sure their setup complies with all applicable federal, state, and local laws.
Building the Blowback 9mm Upper
The 9mm upper is a blowback design.
Unlike a conventional 5.56 AR-15, the barrel does not require the traditional gas block, gas tube, and gas port arrangement.
That simplifies some aspects of the upper while introducing different considerations involving the bolt, buffer, magazines, and ejector.
CMMG 9mm Ejection Port Door Kit
To give the upper a more traditional 9mm appearance, Caleb installs a CMMG 9mm ejection port door kit.
The kit replaces the standard configuration with a Colt-style arrangement incorporating a different deflector and shortened ejection port door.
Once installed, the upper immediately takes on the classic appearance associated with a 9mm AR.
Faxon 8.5-Inch 9mm Barrel
The barrel is an 8.5-inch Faxon 9mm AR barrel.
Because this is a blowback barrel, there is no conventional AR-15 gas system to install.
The barrel provides the compact foundation Caleb wants for the suppressed PCC configuration.
Midwest Industries Suppressor Series Handguard
Surrounding the barrel is a Midwest Industries Suppressor Series handguard.
The larger internal diameter gives Caleb room for the suppressor setup he has planned while maintaining a clean, compact profile.
The combination of the short barrel and suppressor-compatible handguard is central to the overall appearance of the finished PCC.
9mm Muzzle Device Compatibility
Caleb emphasizes an important distinction when selecting a muzzle device for a 9mm barrel.
Thread pitch alone does not establish caliber compatibility. A muzzle device intended for a smaller projectile may share the same thread specification while having insufficient bore clearance for 9mm.
For this project, Caleb uses a 9mm-compatible Dead Air muzzle device and confirms that it is appropriate for the suppressor configuration being used.
Always verify caliber compatibility and follow the barrel, muzzle device, and suppressor manufacturers' specifications.
Dead Air RXD 910Ti Suppressor
The suppressor is a Dead Air RXD 910Ti, developed in collaboration with Ruger.
Caleb pairs it with a Xeno mounting system and positions the suppressor partially beneath the handguard.
The tucked appearance keeps the package compact, but Caleb doesn't want the suppressor permanently buried beneath a long handguard because he still wants convenient access for removal and maintenance.
ModTac Suppressor Shield
The solution is a ModTac suppressor shield.
The shield extends beyond the handguard and covers the exposed portion of the suppressor, giving the build the appearance of a more completely tucked suppressor.
It also acts as a heat shield.
When Caleb needs access to the suppressor, he can remove the shield and then remove the suppressor without taking the entire handguard off the upper.
Backup Sights and Aimpoint Duty
For the sighting system, Caleb adds a rear backup sight to work with the front sight arrangement on the suppressor shield.
The primary optic is an Aimpoint Duty red dot.
Once the upper and lower are assembled, Caleb checks the relationship between the backup sights and the Aimpoint and finds that the setup provides the lower-third co-witness he prefers.
Brownells 9mm Bolt Carrier Group
The upper uses a Brownells 9mm bolt carrier group.
According to the transcript, the BCG is compatible with both Colt- and Glock-pattern magazine setups, making it suitable for the configuration Caleb is building.
The charging handle and BCG receive lubrication before being installed in the upper.
Die Free Co. Accessories
Caleb uses several Die Free Co. accessories throughout the project.
The Tiger Claw serves as a hand stop, while the Quick Stop provides a QD sling attachment point and can also function as a barricade stop.
Caleb positions the accessories based on where his support hand naturally falls rather than installing them according to a predetermined layout.
The goal is to configure the PCC around how it will actually be used.
Fitting M-LOK Hardware Around a Suppressor
A tucked suppressor can reduce clearance beneath the handguard.
Caleb encounters that issue when mounting one of the M-LOK accessories. One of the mounting screws extends far enough inward to contact the suppressor.
The project demonstrates why accessory clearance needs to be checked carefully whenever a suppressor sits beneath a handguard.
Magpul M-LOK Type 2 Rail Covers
Caleb finishes the handguard with Flat Dark Earth Magpul M-LOK Type 2 rail covers.
Rather than covering every available section of the handguard, he places the panels only where his hand actually contacts the firearm.
The result is a functional arrangement that adds texture where it's useful without unnecessarily covering the entire rail.
Completing the 9mm PCC
With the accessories installed, the build is essentially finished.
The combination includes a Brownells AR-15 lower, 9mm hydraulic buffer, Colt-pattern magazines and adapter, Brownells 9mm bolt carrier group, Faxon 8.5-inch barrel, Midwest Industries handguard, Dead Air RXD 910Ti suppressor, ModTac suppressor shield, Aimpoint Duty optic, SBA5 brace, and Die Free Co. accessories.
Caleb finishes by checking the basic operation of the completed firearm.
The only thing left is to take the new 9mm PCC to the range and see how the complete package performs.
If you have questions about the components shown in the build, leave them in the comments or give the Brownells Tech Line a call. We'll be happy to help.
