Requires the use of the .750 gas blockApproximate Weight: 2lbs 8oz. BCMA(R) SS410 Barrels This BCM stripped barrel is machined from a 410 stainless steel. It features hand lapped button rifling with a 1/8 twist rate and M4 feedramps. To give the shooter the best balance of weight and accuracy this BCM Mk12 barrel has a mid-weight profile and a rifle length gas system. (410 stainless is a harder and more corrosion resistant than the conventional 416 stainless found in most barrels.) Requires the use of the .750 gas block.