It is called a "Hand Rifle" in hunting. The 500-grain (32.4g) .45-70 round it fires has a muzzle velocity of 1500 feet per second (500m/s) and has incredible power for a pistol - it can eliminate guards in one shot, regardless of hit location. But the gun's power comes at a price, in the forms of heavy recoil and a single-bullet capacity.
Behind the scenes
This weapon appear in Metal Gear Solid 4: Guns of the Patriots. It cannot be acquired in normal gameplay and must be unlocked through an emblem or a code.