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

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

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BAUs Built to Order - Usually ~3 Weeks
Size Chart

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. 

Returns Policy
You may return most new, unopened items within 30 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.

We can ship to virtually any address in the world. Note that there are restrictions on some products, and some products cannot be shipped to international destinations.

When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.

Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.

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