6.5 ounce pistol caliber buffer. 9mm/40s&w/357sig. This 6.5 ounce Pistol Buffer is the correct weight to ensure reliable cycling of your blow-back operated AR-15 pistol caliber build. This buffer is machined from steel, and coated with a wear resistant finish. Your firearm will be more reliable, smoother shooting, and have less felt recoil using the heavy buffer over a standard buffer. It is compatible with any AR15 pistol caliber upper with barrel lengths for 3-16 inch.