Requires the use of the .750 gas block or front sight baseApproximate Weight: 3lbs 3oz. SAM-R barrel with Service Match Heavy Contour 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 accuracy this BCM SAM-R barrel has a service match heavy 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 or front sight base.