ARAK-21 Caliber Conversion Kit - Complete w/ Bolt & Firing Pin

BAUs Built to Order - Usually ~3 Weeks
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Note- This kit is appropriate for an ARAK owner who does not have the bolt for their new caliber. Of note, 5.56 and 300 BLK are interchangeable. 7.62x39 has its own bolt. For just the BAU, see the BAU Only product listing. 


Kit Includes:

  • BAU of Customer's Choice
  • Complete ARAK-21 Bolt
  • Firing Pin

ARAK-21® Barrel Assembly Unit Technical Description.

  •  -The ARAK-21® Barrel Assembly Unit (BAU) is comprised of the barrel, barrel trunnion, gas block, gas tube, gas adjuster, and the muzzle brake.
  • -Barrels are made from resulphurized 4150 CMV GBQ (Gun Barrel Quality) MIL SPEC mil-B-11595-E Pre Heat Treated 28 – 32 Rc Steel or 416-R Stainless Steel


-All ARAK-21® barrels are manufactured at Faxon Machining in Cincinnati, OH. 

  • -All barrels are gun drilled, gun reamed, and button rifled.
  • -All barrels are nitrided using a Quench / Polish / Quench (QPQ) process.
  • -Barrels are currently available in 12 ½”, 16”, and 20” lengths. (12.5 & 16" for 7.62x39)
  • -Barrels are currently available in both .223 /5.56 Caliber 1 in 8 twist, and 300 BLK & 7.62x39 caliber barrels in 1 in 8 twist.
  • -5.56 caliber barrels are threaded with a ½” – 28 UNF thread at the muzzle.
  • -300 BLK & 7.62x39 barrels are threaded with a 5/8” – 24  UNF thread at the muzzle.
  • -Each gas block and gas adjuster knob has four settings,  three allowing variable gas flows and one blocking gas flow for single shot operation.
  • -The 5.56 & 7.62x39 gas adjuster knob is inserted and removed by rotating into position and either pushed or pulled.  There are detents to identify the 4 gas selections. 300 BLK has three settings: low, high, and off. 
  • -The BAU is connected to the upper receiver with “Keys” and is held in place by the pivot pin, and the lower forearm.
  • -The gas block on the ARAK-21® BAU has a clean out port between the gas cylinder, and the barrel.
  • -300 BLK & 7.62x39 Caliber BAU’s have a unique profile on the barrel forward of the gas block to identify the caliber by both sight and touch.
  • PLEASE NOTE:Images shown may include items not sold with the ARAK-21® Upper Receiver.


Faxon Technical Note on 7.62x39 Caliber Kit:

  • The factory recommends a high-power hammer spring to use with the 7.62x39 kit. 
  • Many aftermarket "light" triggers will not reliably ignite 7.62x39 surplus ammunition.  
  • A spring is included and installed on XRS rifles ordered with the caliber. It is sold separately for the upper or caliber kit only. 
  • Faxon offers a Wolff high power spring for sale. 
  • Faxon recommends HiperFire triggers with a special spring kit for an improved trigger pull. Contact HiperFire for details.

300 BLK Compatibility:

Due the fixed gas system length of the ARAK platform and variability of 300 BLK subsonic ammunition, a suppressor is required for reliable function with the 300 BLK BAUs using subsonic ammunition and supersonic on the 12.5" barrel.