The Radical Firearms 16, Forged 5.56mm AR rifle uses MIL-STD Upper and lower receivers along with their 15, thin free float rail system for increased accuracy, keeping your hands cool, and giving you plenty of room for accessories. The B5 Grip and Stock provide a comfortable hold on the rifle whether prone or upright.The Radical Firearms 16, Forged .300 blackout AR rifle uses MIL-STD Upper and lower receivers along with their 15, thin free float rail system for increased accuracy, keeping your hands cool, and giving you plenty of room for accessories. The B5 Grip and Stock provide a comfortable hold on the rifle whether prone or upright.