The EPC-9 upper receiver is the perfect addition to any AR9 build. Including a last round bolt hold open mechanism and compatible with most standard AR15 barrel nut and handguard combinations this upper receiver will help take your pistol caliber build to the next level. Features: Last round bolt hold open mechanism, Accepts most AR15 compatible barrel nuts and handguards, Dimple above threads to allow for proper handguard timing, Standard AR15 takedown/pivot pin lug pattern, Machined from custom forged 7075-T6 aluminum, Laser engraved T-marks. Includes: Upper Receiver, Pre-Installed last round bold hold open assembly.