Arms Unlimited Colt MK12 HBAR 18″ Upper Receiver Assembly

Sold exclusively by Arms Unlimited during 2018/2019. The flat top upper receiver comes with a factory installed MK12 MOD1 12-inch Knights Armament free float RAS quad rail. The barrel is Colt’s 18″ 1:9 heavy stainless steel accurized precision rifle barrel threaded in 1/2×28 with an A2 flash hider included. Utilizing a rifle length gas system and a low profile gas block.

Package Contents

Colt MK12 HBAR Complete Upper Assembly

Complete M4 Full Auto Bolt Carrier Assembly

Knights Armament Free Float RAS Quad Rail

Rifle Length Gas System

Charging Handle

Low Profile Gas Block


Accurized 18 Inch 1/9 twist 5.56mm NATO Stainless Steel MP tested barrel

Unique direct gas operating system eliminates the conventional operating rod and results in fewer and lighter components

Accommodates the full range of 5.56mm ammunition, including NATO MK262, M855/SS109 and U.S. M193

Flat top receiver allows for easy mounting of optics

Caliber – 5.56mm

Gas Direct System, Rifle Length

1/2×28 Thread Pattern

Price at time of this post is $999.00 (price is for historical reference only)