Pro2a Tactical line of Non Reciprocating (NR) Side Charging AR-15 Complete Uppers feature the Gibbz Arms G4/G9 upper receivers. Non reciprocating keeps the charging handle forward during cycling. It uses standard AR-15 BCGs without any modification. All that is required is to swap out the cam pin with the Gibbz enhanced cam pin that will be included. Premium Side Charging Uppers made in the USA.