M4-type barrel extension has NiB-X finish that aids in smooth locking and unlocking with the bolt, consistent feeding and helps prevent hang-ups. This high-tech coating lasts the life of the weapon, and won’t rub off, flake off, or gall. Helps dissipate heat for cooler operation, too. Precision machined from 8620 steel to USGI specifications with integral M4-type feed ramps and predrilled locator pin hole. DPMS Pattern.