AR15 45acp barrels by Rhineland Arms are designed for blowback conversions. These have an accurate chamber and a polished and beveled feed ramp into the chamber. Available in 16.5″ and 6.5″ lengths. All AR barrels include a 5/8-24 muzzle thread and a QPQ finish over 4150 steel.
6.5″ barrels are priced at $55 each.