Milspec 4150 alloy that has been melonite treated (see faq section for info on this). Upgraded SpecII chamber with 1:11 twist rate. Gas block diameter is .750 and barrel is threaded 5/8×24. Mid length gas. Barrel extension has M4 feedramps to assist in feeding reliability. These barrels are very accurate and can obtain MOA/Sub-MOA with good ammo and a good shooter.