RRA LAR-PDS Carbine is one of a new generation of firearms employing RRA's patent-pending Piston Driven System (PDS). Featuring a purpose designed bolt carrier, an adjustable gas piston and an over-the-barrel spring and guide rod arrangement, the RRA LAR-PDS is able to completely do away with the traditional recoil system associated with AR-style firearms, making for an extremely versatile weapon platform.