Machined top to bottom from 7075-T6 aluminum, a peak-strength corrosion-resistant aluminum alloy A hard coat anodize finish per MIL-A-8625, the anodizing model for most military and aerospace products Full compatibility with all mil-spec internal parts Full compatibility with all other aftermarket mil-spec upper receivers Full compatibility with GI standard issue magazines as well as PMags Multi caliber mark This is Overthrow. An open mag well helmet design, with battle worn dents, sword gashes and crack lines. Leave it anodized black, give it a Spartan style, a Viking theme ... the customization opportunities with this one are endless.