DD MK12 SPR URG 5.56 18" BLACKDANIEL DEFENSE MK12 SPR URG 5. 56 18" BLACK The MK12 AR15 style Upper Receiver Group is constructed around an 18 inch Stainless Steel barrel with a chamber created during the Cold Hammer Forging process, which ensures the most precise alignment of the chamber to the bore possible. This, along with being DLC finished, equates to unprecedented accuracy and durability. The MK12 barrel is engineered with a rifle length direct impingement gas system and