This BCA AR-15 complete 6mm Arc upper has a 18" heavy contour barrel with a parkerized finish, and features a 1:8 twist rate, with a mid length gas system. It includes a 15" MLOK rail, an M4 flat-top billet upper receiver, a BCA bolt carrier group, a flash hider, and a right-side charging handle (Gen 2) (patent protected). This 6mm Arc upper is compatible with any mil-spec AR-15 lower. Check out Magazines here! {{widget type="Magento\Cms\Block\Widget\Block" template="widget/static_block/default.phtml" block_id="56"}} *Note - We strive to provide the most accurate photographs of our product. Variations may occur in the skeletonized section of the handguard/flash hider you receive. {{widget type="Magento\Cms\Block\Widget\Block" template="widget/static_block/default.phtml" block_id="42"}} It is the responsibility of the consumer to ensure all state, local, federal, and ITAR regulations are followed