All lower parts are standard AR-style parts, and are interchangeable with other standard GI (non-Colt's) parts. The upper is a modified component that contains the famous OA-series recoil system that eliminates the need for a buffer tube or standard recoil system of any type. There is virtually no recoil due to the gas-op OA style system, but it still packs the punch of the .223 Remington centerfire rifle cartridge.
