The Faxon ARAK-21® 12.5" 5.56 NATO Barrel Assembly Unit (BAU) is a complete, self-contained module designed for rapid barrel swaps on the ARAK-21® upper receiver. This heavy-profile assembly integrates the barrel, gas block, muzzle brake, gas piston, adjustable gas regulator, and barrel trunnion — delivering reliable long-stroke piston operation in a compact, interchangeable format. Ideal for tactical, defensive, and multi-caliber builds where quick caliber changes and piston-driven reliability matter most.

Key Benefits

• Modular BAU design: Quick-swap barrel assembly for the ARAK-21® — change barrels in seconds with minimal tools.
• Long-stroke gas piston system: Adjustable 4-position gas regulator (3 flow settings + off for single-shot) for tuned reliability and suppressor use.
• Heavy profile barrel: Enhanced durability and heat management in a short 12.5" configuration for compact handling.
• Premium materials: Gun-drilled, reamed, button-rifled from high-quality 4150 CMV steel, fully QPQ black nitride finished for corrosion resistance and longevity.
• Integrated components: Includes gas block with clean-out port, piston, adjustable gas knob, muzzle brake, and trunnion — all pre-assembled.
• Precision manufactured: Made in Cincinnati, OH by Faxon — ensures consistent accuracy and performance in the ARAK-21® platform.

Specifications

Why Choose the ARAK-21® Barrel Assembly Unit

The ARAK-21® BAU enables true modular performance in a piston-driven platform — swap barrels/calibers quickly without tools, enjoy adjustable gas for optimized cycling (including suppressed use), and benefit from the hybrid AR/AK-inspired reliability. The 12.5" heavy profile delivers compact maneuverability with enhanced durability, making it perfect for short-barreled defensive setups or multi-caliber experimentation on your ARAK-21® system.

Installation & Compatibility

• Designed exclusively for the ARAK-21® upper receiver — installs via pivot pin and forearm keys in seconds.
• Integrated long-stroke piston and adjustable gas block — supports suppressed fire and tuned operation.
• Includes pre-installed muzzle brake; compatible with ARAK-21® bolt carrier and recoil system.
• SKU: ARAK21BAUONLY-104S-12 — UPC: 816341029194 — for 5.56 NATO use only.

Frequently Asked Questions

Overview: ARAK-21® 12.5" 5.56 Barrel Assembly Unit

The Faxon ARAK-21® 12.5" 5.56 NATO Barrel Assembly Unit provides modular versatility and piston-driven reliability in a compact heavy-profile design. Manufactured with precision gun-drilling, button rifling, and QPQ nitride finish, it integrates all key gas system components for quick installation and superior performance.

Every ARAK-21® BAU is built at Faxon Firearms for consistent quality, with an adjustable long-stroke piston system that offers 4 gas settings for optimized cycling across various conditions. Whether upgrading your ARAK-21® setup, adding a short-barreled configuration, or enabling fast caliber swaps, this BAU delivers innovative value from Faxon Firearms.