MARS-L MRP 5.56X45 NATO SEMI-AUTO RIFLE MRP Upper Receiver | Ambidextrous Charging Handle | S-A Bolt Carrier Group | MARS-L Lower Receiver | 16a ^2 5.56A-45 (.223) Chrome Lined 1:7a ^2 RH Twist Barrel Utilizing the LMTA(R) patented Monolithic Rail Platform, MRP(TM). The only true monolithic rail platform, milled from a single solid piece of aerospace aluminum forging. It utilizes two locking bolts accessible from the side of the receiver to lock in the barrel extension. This patented technology engages the barrel extension for a full 360 degrees around the extension and makes the barrel removable within seconds with a return to zero of the same barrel. O Mfg: Lmt Defense