Faxon Firearms Arak-21 Urssb556 Arak 21 16 5.56 Cmp Upper

The Faxon Firearms ARAK-21 16" 5.56 complete upper receiver is a modern, self-contained alternative to the traditional AR-15 platform. Built as a piston-driven system, it mates to any standard AR-15 lower with just two pins—takedown and pivot—and requires no tools to install or remove. Swap your upper in under a minute, then strip it just as quickly. If you run a standard AR-15 lower and want to upgrade to piston reliability without buying a whole new rifle, this upper does exactly that.

The heart of the ARAK-21 is its gas piston design and unique Barrel Assembly Unit (BAU). The BAU bundles the barrel, gas block, muzzle brake, gas piston, and adjustable gas knob into a single unit; the gas knob itself is the only removable component. Four detent settings let you dial in gas flow for different loads, or lock it down for single-shot operation. A field-accessible clean-out port between gas cylinder and barrel simplifies maintenance. The bolt carrier rides on bolted-in hardened steel rails rather than the receiver itself, creating a metal-on-metal wear surface that runs smoother and lasts longer.

The receiver itself is a one-piece, aircraft-grade 6061-T6 aluminum billet with a full-length picatinny rail on top (laser-engraved for optic placement) and three additional rails at the muzzle—full M4-style quad configuration. The ambidextrous, non-reciprocating charging handle folds and relocates left-to-right without tools. Bolt is an eight-lug design with involute profile; the self-contained firing pin retention system eliminates the need for a cotter pin. Note: most ARAK-21 components are proprietary and not interchangeable with standard AR-15 uppers; only the firing pin, extractor spring, and ejector spring swap across platforms.

This upper ships with one Barrel Assembly Unit, an owners manual, two Allen wrenches for forearm and rail screws, a standard charging handle, a lower forearm, three aluminum rails, three insulating shims, bolt carrier assembly, and a dual recoil spring system. The recoil system stays within the upper receiver, so you can add a folding stock to your lower if you choose.

Key Features

• Gas piston long-stroke system with three variable gas settings plus single-shot mode
• Barrel Assembly Unit pre-assembled and ready to run—field-serviceable gas adjuster knob only
• One-piece 6061-T6 aluminum receiver with full-length top rail and quad-rail muzzle configuration
• Ambidextrous, non-reciprocating, tool-free relocatable charging handle
• Eight-lug bolt with involute profile; hardened steel rail system for smooth carrier travel
• Self-contained firing pin retention; no cotter pin required
• Direct AR-15 lower compatibility—installs with takedown and pivot pins only
• Field-accessible gas block clean-out port
• Compatible with folding stocks due to self-contained recoil system

Specifications

Caliber	5.56 NATO
Barrel Length	16 inches
System Type	Gas piston, long-stroke
Receiver Material	Aircraft-grade 6061-T6 aluminum, one-piece billet
Bolt Design	Eight-lug with involute profile
Gas Adjuster	Four settings (three flow levels + single-shot/blocked)
Charging Handle	Ambidextrous, non-reciprocating, folding, tool-free relocation
Rail System	Full-length top Picatinny (Mil-STD-1913), three additional Picatinny rails at muzzle
Lower Receiver Compatibility	Standard AR-15
Installation	Takedown pin and pivot pin only; under one minute, no tools

Frequently Asked Questions

Will this ARAK-21 upper fit my AR-15 lower?

Yes. The ARAK-21 upper is designed to interface with any standard AR-15 lower receiver using only the takedown pin and pivot pin. Installation takes less than a minute and requires no tools.

What comes in the box with the ARAK-21 upper?

This package includes one Barrel Assembly Unit (barrel, gas block, muzzle brake, gas piston, and gas adjuster knob pre-assembled), the complete upper receiver with charging handle, a lower forearm with screws, three aluminum full-length Picatinny rails, three insulating shims, bolt carrier assembly, lower recoil lug with spring guide rod, dual recoil spring system, owners manual, and two Allen wrenches for installation.

Can I adjust the gas on the ARAK-21?

Yes. The gas adjuster knob has four settings: three allow different gas flows for optimized operation with various ammunition types, and one blocks gas flow entirely for single-shot operation. A field-accessible clean-out port between the gas cylinder and barrel simplifies maintenance.

Are ARAK-21 parts interchangeable with standard AR-15 uppers?

Mostly no. Due to the ARAK-21's unique piston design and billet receiver, very few components cross over to standard AR-15 uppers. Only the firing pin, extractor spring, and ejector spring are standard and interchangeable with AR-15 upper receivers.