Buffalo Bore Ammunition Standard Pressure 45 Auto Rim 255 Gr Hard Cast. It is the ballistic equivalent of +P 45 ACP loads yet they operate at standard 45 ACP pressures. These 45 Auto Rim loads are safe to use in any 45 ACP revolver that is in normal operating condition including any model 1917 Colt or S&W revolver. Specifications for Buffalo Bore Ammunition 31A/20 Standard Pressure 45 Auto Rim 255 Gr Hard Cast F: Manufacturer: Buffalo Bore Ammunition Caliber: .45 Auto Rim Number of Rounds: 20 Bullet Type: Hard Cast Flat Nose (HCFN) Bullet Weight: 255 grain Cartridge Case Material: Brass Muzzle Velocity: 850 ft/s Application: Protection Primer Style: Centerfire What is Buffalo Bore Ammunition 31A/20 Standard Pressure 45 Auto Rim 255 Gr Hard Cast F good for? The manufacturer thinks that it is good for protection.