Complete, ready-to-install, semi-auto receivers let you change your AR-15 from a sporter to a match rifle or long-range varminter in just minutes-or add to a lower receiver to complete a parts gun. All barrels have six-groove, 1-9″ right-hand twist rifling and M4-type feed ramp. Pre-ban style standard (Std) barrels are chambered for 5.56mm NATO, with A2 flash suppressor, military-style polymer handguard, and A2 front sight housing that includes bayonet lug and riveted sling loop. AP4 adds to Std configuration the cutout for M204 grenade launcher mount to replicate the contours of the USGI M4 carbine barrel. Mfg: Dpms SPECS: Receiver – aluminum, anodized and Teflon coated, black. AP4 – 4140 steel, Parkerized finish, dark gray. .725″ dia. at muzzle.