The most important part to consider when building any AR15 rifle is the complete upper receiver. The upper receiver assembly contains all of the essential parts of the rifle including the barrel, bolt carrier and firing pin, among others. AR uppers help you customize a rifle for any application whether it is military or civilian. For instance, an A3 upper receiver is flat-topped to accept a range of scopes for hunters along with the A4 upper receiver they both use a gas block or a standard front sight.
For the widest selection of complete upper receivers with a tight fit and no wobble, check out the options available from Right to Bear Arms and Supply. You can choose from mil-spec upper receivers which are forged uppers. In addition, we have billet upper, M4 flat-top upper, AR15 striped upper or Spikes upper. Two popular models are the Aero Precision with forward assist & ejection port door and the BCM M4 with laser T-marks.