The patented LMT Monolithic Rail Platform (MRP) upper receiver is the only AR-15 upper that incorporates the handguard and receiver as one component. This state-of-the-art design is CNC machined from a single piece of forged aerospace aluminum resulting in benefits and functionality unmatched in the industry. Integrating this upper receiver with an MRP barrel creates an incredibly simplistic modular platform in which the barrel is held in place with a proprietary locking system utilizing two locking bolts on the right side of the receiver. Barrel swaps and caliber changes are easily completed in a few minutes with only a T-30 Torx bit and torque wrench (a factory pre-set torque wrench is available). Additionally, since the handguard is integral to the receiver you will not experience shifts in point of impact while using aiming devices that are attached directly to the handguard. Nor will you need to purchase expensive cantilever optic mounts. This receiver utilizes the patented LMT MRP barrels and like the other carbine length MRP receivers, is designed for use with either their piston barrels or direct impingement barrels in lengths from 10.5" to 18".