Complete 5.56 Nato pistol length upper has a 12.5" barrel.This features a 1:7 twist rate, with a mid-length gas system. It includes a 11.5" MLOK rail, an M4 flat-top billet upper receiver, a BCA bolt carrier group, a flash hider, and a right-side charging handle. Anderson's lower receivers are CNC machined from a high-strength, 7075 T6 aluminum forging for reliable performance and outstanding durability. Machined to military specifications & standards and marked "Multi-Cal" to be used with multiple calibers on the AR-15 platform. This Lower Receiver comes in type III black hard anodize.