XTS Complete Upper Receiver w/o BCG w/ Ce Rail USA Edition AR-15 16.5in 7.5in Barrel Pistol 1-7 Twist 1/2x28 Thread M-LOK Stainless Steel Bird Cage. 5in 5.56 upper comes FULLY ASSEMBLED with a 5.56 NATO barrel capable of shooting both .223 and 5.56....