Spike's Tactical Complete Upper Receiver, 223 Rem/556NATO, 16 FN Hammer Forged Barrel, 1:7 Twist, Fits AR Rifles, Mid-length Gas System, Front Sight Post, Black Finish STU5435-MLS Spikes complete upper assemblies will arrive to you inspected" tested" and ready to drop-in and go to work. Spikes maintains the same high standard of tolerances and attention to detail as the uppers they use for complete rifle builds. Every built upper and complete gun is test fired before leaving Spikes facility for function check before it reaches you.