6.5 ounce extended length 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. It requires no spacer since it is an extended length buffer. The extended length also limits travel so it build does not prematurely wear or break your bolt catch. 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.