AR9 Build Basics

AR9 features basically the same ergonomics as the AR15. However, to build an AR9, these parts look similar but they are completely different. Here is the AR9 build basics guide that covers everything from upper receiver and lower receiver parts.

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AR9 Build Basics

AR9 is basically 9mm pistol caliber carbine in the AR platform. There are pros and cons from its centerfire AR15 including weight, ammo availability, aftermarket support and ballistic performance.

While most AR9 designs take standard Glock magazines, which makes it a very popular choice compared to other pistol caliber carbines with expensive proprietary magazines. For shooters who want to standardize their gear selection and train with the same equipment over and over, the AR9 is a great option. 

AR9 can be purchased or build in either pistol form or short barrel rifle form (NFA compliance required).


AR9 Blowback System

The AR9 is a direct blow back system without the gas block or gas tube to cycle the bolt like an centerfire 5.56 AR15. The force of the bullet going down the barrel pushes the bolt back.

ar9 bolt carrier group

In a basic blowback firearm system, there's no mechanical lock to keep the breech shut during firing. When fired, the bullet moves forward due to gas pressure, while the empty cartridge is pushed backward.

It's crucial to limit the cartridge's movement until the bullet exits the barrel and pressure drops. If not, the cartridge might burst, scattering fragments and gas, risking injury.

The system uses a heavy buffer and bolt to delay the cartridge's exit. This ensures the bullet leaves the barrel safely before the cartridge moves significantly.

AR9 Fire Selector

AR9 fire selector is the same as the ones on an regular AR15. There are many options available on the market. Users can use the standard 90 degree throw or upgrade to the popular 45 degree short throw fire selector.

radian talon safety selector

While the 45 degree fire selector allows the shooter to switch between safe and semi by reducing the amount of thumb movement, and maintain the grip. 

AR9 Bolt Release

The AR9 bolt release is the same as AR15. The bolt release functions as the mechanism to manually lock the bolt open, or lock the bolt open when the magazine is empty.

In addition, battery assisted device can be installed on a AR9 for faster reloads.

AR9 Triggers

ar9 lower receiver

Given the blowback operation of most AR9s, the trigger should be robustly built to handle the increased forces. A good PCC trigger should have a clear and positive reset. This ensures that the shooter can feel when the trigger is ready to be pulled again, which is crucial for rapid firing. It's the same thing expected from most firearms.

Many modern trigger upgrades come in a "drop-in" design, which makes installation much easier when all the components are already contained in a housing unit, and then it goes into the lower receiver with two pins to secure it in place.

Given the unique stresses that PCC triggers face, especially in AR9 platforms, it's essential to invest in a trigger made with durable materials and designed for longevity.

Some of recommended triggers are:

AR9 Upper Receiver

The AR9 upper receiver barrel nut is the same as AR15. Any AR15 handguards can be used on an AR9 with the appropriate length. The user can mount any accessories on it including foldable sights, foregrip and more.

v7 system handguard

The ejection port size is obvious different. It's smaller for the 9mm casing. 

The charging handle is compatible with most AR15 charging handles, and they are interchangeable. The AR9 bolt features a gas key alike extrusion for the charging handle to grab onto.

AR9 Lower Receiver

psa px9 lower receiver

The AR9 lower receiver accepts most 9mm or 40SW Glock style magazines. It's not a Glock magazine magwell adapter that goes on a standard AR15 lower receiver.

The receiver can accept standard pistol grip, buffer system and stock.

Some options like the Colt style 9mm AR9 receivers take 9mm Colt magazines instead of Glock. So if you buy a lower receiver, please be aware of that specification.

Check out lightweight stocks here

Build AR9 Or Buy Complete?

Building a custom AR9 can be appealing due to potential cost savings compared to buying a finished one from a major brand. Some enthusiasts prefer crafting a unique 9mm AR or relish the challenge. 

Many have successfully built theirs with minimal issues. However, others have faced significant challenges, leading to unexpected time and money investments. They might end up replacing numerous parts, buying tools, spending on ammunition and range visits, and taking months to perfect the build. Sometimes, the costs can even surpass that of a premium 9mm AR.

Opting for a complete 9mm AR from a reputable manufacturer can offer advantages. These companies have already tackled the challenges of ensuring the parts work seamlessly. Plus, if issues arise, their warranty typically covers repairs, saving you the troubleshooting hassle.

AR9 Interesting Facts & User Experience

Colt's AR-pattern 9mm Blowback Design

  • Colt introduced the AR-pattern 9mm blowback SMG/carbines in the 1980s.
  • These firearms have a 15.9 oz. bolt and a 5.6 oz. sliding-weight buffer, totaling 21.5 oz.
  • Components include an aluminum buffer spacer, standard carbine spring, and carbine buffer tube.
  • The magazine design is similar to the Uzi but has a new mag catch and a last-round bolt hold-open feature.
  • Initially, solid steel buffers were used, but due to performance issues, sliding weight buffers replaced them.

Technical Specifications and Features

  • The 9mm bolt, shorter than the 5.56mm version, looks like a 5.56mm carrier without an extended bolt.
  • A buffer spacer in the recoil spring prevents the bolt from retracting too much, avoiding potential damage.
  • Extended buffers, around 4.0” long, are available, making buffer spacers unnecessary.
  • The ideal combined weight of the bolt and buffer for best performance is between 22 oz. and 24 oz.

Market Trends and Maintenance

  • Bolts available in the market usually weigh between 12oz. and 15.5oz.
  • 9mm buffers can weigh up to 12 oz., with the older 5.6oz. version deemed unsuitable for contemporary 9mm bolts.
  • Aluminum ammunition is discouraged for blowback systems.
  • Blowback systems need frequent cleaning due to quick dirt buildup and potential wear on components.
  • Common issues with 9mm blowbacks involve ejection and bullet feeding.
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