Radical Firearms RF-15, Semi-automatic, 6.8 SPC, 16 Heavy Barrel, 1:11 Twist, Mid Length Gas System, B5 Stock, B5 Grip, A2 Flash Hider, 15 RPR M-LOK Handguard, 15Rd, Black RF00109 The Radical Firearms 16" 6.8 SPC II AR rifle uses MIL-STD Upper and lower receivers along with their 15" RPR free float rail system for increased accuracy, keeping your hands cool, and giving you plenty of room for accessories. Regardless of if it's your first or fiftieth, a Radical Firearms AR rifle will not disappoint!