Brownells BRN-180 Upper Receiver Specs Type: Short-stroke piston-operated semiautomatic Caliber: .223 Wylde chamber handles both .223 Rem. and 5.56 NATO Capacity: 25-round detachable box magazine Barrel: Nitrided 16 in., button rifled 1:8 twist; threaded 1/2x28; 3-prong flash suppressor...