This is a KE Arms KP-15 Lower with SLC AR57 Five Seven Semi-Automatic Rifle Upper Receiver AR57 16-inch Complete ULT M-LOK Upper designed to convert a compatible AR-15 lower to fire 5.7x28mm ammunition. This upper feature a 16-inch barrel with a perforated muzzle brake on 1/2x28 threads, an 18-inch overall barrel length, an 8620 alloy bolt, and a durable melonite finish. Includes one 50-round magazine. Lower Receiver * KP-15 monolithic polymer AR-15-style lower receiver made from injection-molded 30% glass-filled nylon * Integrated buttstock, buffer tube, pistol grip, and trigger guard for a streamlined, durable design * Reduced weight compared with similarly configured traditional receivers * Lower overall cost compared with similarly configured builds * Integrated construction helps reduce subcomponents and improve production efficiency during high-demand market cycles Included One 50-round magazine SKU# 326427 RR