The Faxon ARAK-21 is a gas-piston-driven complete upper chambered in 5.56 NATO with a 12.5-inch, nitride-finished barrel from Faxon Firearms (brand part no. URSSB556P). It interfaces with a standard AR-15 lower through only the takedown and pivot pins, installing in under a minute with no tools and no modification to the lower receiver. A 4-position gas adjuster knob tunes gas flow across three settings, plus a fourth that blocks gas flow for single-shot operation, and the upper ships complete with charging handle, bolt carrier assembly, and three full-length Picatinny rails. Because the design is largely proprietary, only the firing pin, extractor spring, and ejector spring interchange with a standard AR-15 upper.

Key Specifications

• Chambered in .223 Remington/5.56 NATO.
• Barreled at 12.5 inches with a 1:8 twist.
• Barrel finished in nitride for wear and corrosion resistance.
• Operates on a gas piston system rather than direct impingement.
• Interfaces with a standard AR-15 lower using only the takedown and pivot pins, with no lower modification required.
• Installs in under a minute with no tools.
• The gas adjuster knob offers 3 gas-flow settings plus a 4th setting that blocks gas flow entirely for single-shot operation.
• Includes three aluminum full-length Picatinny rails.
• Ships with a charging block and charging handle, bolt carrier assembly, and dual recoil spring system.
• Only the firing pin, extractor spring, and ejector spring interchange with a standard AR-15 upper; most other parts are proprietary to the ARAK-21 system.

Frequently Asked Questions

Can I install this on my existing AR-15 lower without modification? Yes, the ARAK-21 interfaces through just the takedown and pivot pins, with no change needed to a standard AR-15 lower.

How does the gas adjuster work? The 4-position knob offers three gas-flow settings plus a fourth that blocks gas flow for single-shot operation.

What parts interchange with a standard AR-15? Only the firing pin, extractor spring, and ejector spring; the rest of the system is proprietary to the ARAK-21 design.

Buy the Faxon ARAK-21 Complete Upper

Add a piston-driven ARAK-21 upper to your AR-15 lower with zero modification required. Order it from our Lubbock, Texas gun shop, and browse our AR15 uppers selection for more AR15 uppers.