The AR15 Stripped Upper Receiver is one of our most popular products. Forged from 7075-T6 aluminum, this stripped upper is precision machined to mil-spec M16/M4 specifications. Match this upper with one of our AR15 lower receivers for a solid and dependable fit. XL model has a larger door port to allow usage for 5.56 builds or all additional AR15 platform calibers to include the larger .458 SOCOM and other similar rounds (.450 Bushmaster, .50 Beowulf, etc) WITHOUT needing port door size enlargement modification!