This Alexander Arms AR-15 Precision Upper Receiver comes fully assembled and ready to install on any standard small pin lower receiver. Chambered for the awesome 50 Beowulf cartridge, this upper squeezes 50 caliber firepower into a standard AR-sized envelope, offering shooters an immense step up the power scale compared to a traditional 223 Remington. With its compact and maneuverable 16.5" Barrel and Free Float Tube Composite Handguard, this precision upper configuration is perfect for use as a close- to medium-range hunting setup that's capable of taking down the largest of game. It features a Forged 7075-T6 Aluminum Flat-Top Receiver for adding optics and/or iron sights, a low profile gas block, complete bolt carrier group, charging handle, one 7-Round Magazine and an enormous Tank Muzzle Brake that decreases felt recoil upon firing by as much as 40-50 percent. Upper does not have an ejection port door.