Description The Aero Precision M5 Complete Upper is an assembled upper receiver designed around a 16-inch .308 Win barrel and an ATLAS R-ONE handguard. This upper ships assembled and includes a mid-length gas tube and low-profile gas block, plus a port door and forward assist. The assembly does not include a bolt carrier group (BCG) or charging handle. Key Specifications The caliber is .308 Win. The barrel measures 16 inches. The rifling twist is 1:10″. The barrel finish is matte black. The muzzle threads are 5/8-24. The handguard is an ATLAS R-ONE attachment system. The gas system uses a mid-length gas tube with a low-profile gas block. The upper ships assembled. Includes port door and forward assist. Other features include M4 feedramps. Built around a stout 16-inch .308 configuration and a slim, lightweight ATLAS R-ONE handguard, this assembled M5 upper is suited to AR-10 style precision and field use where a compact, mid-length gas configuration is desired. Its assembled state and M4 feedramps simplify integration into compatible builds while the low-profile gas hardware keeps the front end streamlined for optics and accessories.