The .45 Colt (often incorrectly called the .45 Long Colt), was introduced in the single action Colt revolver in 1873. Two years later, it was adopted by the U.S. Army and served there until it was replaced by the less powerful .38 Long Colt in 1892. Originally loaded with a 255 grain lead bullet pushed out the muzzle at 810 fps by 40 grains of black powder, the big cartridge generated a then impressive muzzle energy of 378 foot pounds. Today, Colt's .45 caliber cartridge is loaded with smokeless powder to a nominal muzzle velocity of 855 fps with 250 and 255 grain bullets and a 225 grain bullet at 900 fps. During its heyday, the .45 Colt was the magnum of revolver cartridges. Only the .44 Specialwith its 360 foot pounds of energy came close to matching its punch. Even though the various modern day magnums have pushed the old 45 to the bottom of the performance charts, it still has enough life left to be used for hunting game up to whitetails in size at woods ranges. A 250 grain bullet loaded to about 1000 fps and fired in a modern revolver such as the Ruger Blackhawk delivers about as much energy at 50 yards as does the .357 Magnum, and it punches a much bigger hole through things once it gets there. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.