The Gibbz Arms G4 side charging upper receiver is a non-reciprocating upper receiver that uses most standard AR-15/M16 bolt carrier group. The only change needed is to replace the standard cam-pin with the included replacement enhanced cam-pin. The upper receiver features a detent to keep the charging handle forward during operations; a bolt carrier door in the rear that allows for easy bolt carrier removal yet keeps dust and debris out, a beveled ejection port, and charging handle dust cover.