This Bear Creek Arsenal AR-15 7.5" M4 profile parkerized 10MM barrel has a blowback gas system with a 1:16 twist. Our AR-10MM parkerized rifle barrels are made from the finest 4150 Chrome Moly Vanadium and precisely rifled for high accuracy at a great price. Use a Bear Creek Arsenal ar barrel in your next AR build and experience superior performance backed by a lifetime warranty! {{widget type="Magento\Cms\Block\Widget\Block" template="widget/static_block/default.phtml" block_id="42"}} Does not include gas block or gas tube