Windham Weaponry's RP9 AR pistol in 450 Bushmaster features a laser-engraved caliber mark on the left upper receiver. The 9" melonite QPQ-finished barrel has a 1:24" twist with a .450 compensator and a 7" free-float handguard. The flattop receiver is forged from 7075 T6 aluminum with a black hardcoat anodized finish, features an aluminum Magpul enhanced trigger guard, and has polymer front and rear flip sights. This semi-automatic uses a gas impingement system. It is fitted with an SB Tactical pistol arm brace, Hogue beavertail pistol grip, and a 5-round magazine.