The first Colt Single Action Army prototypes were manufactured in .44 American caliber for the 1872 government trials, as the .44 American was the cartridge used in the 1,000 Smith & Wesson Model 3 revolvers issued to the troops.
After the tests, the Colt was declared the superior revolver and the government specified that a .45 caliber cartridge would be required.
With the adoption of the Colt Single Action Army revolver in 1873, the service cartridges were Copper-cased .45 centerfire Benét inside primed "Colt's Revolver Cartridges" loaded with 30 grains of black powder and an inside lubricated bullet of 250 grain.
They were manufactured at Frankford Arsenal, Philadelphia, PA, through 1874.
In 1875, the cartridge was shortened so that it would also function in the newly adopted S & W Schofield revolver.
It was designated "Revolver Cartridge" and loaded with 28 grains of black powder and a bullet of 230 grain.
The Bénet-primed cartridges were manufactured until 1882 and then replaced by reloadable cartridges with brass cases and external primers.

The original .45 Colt black-powder load of 40 grains propelled the 250–255 grain bullet at a nominal 970 feet per second (300 m/s).
Authors John Taffin and Mike Venturino have demonstrated that modern black-powder loadings of the .45 Colt cartridge frequently achieve velocities in the vicinity of 1,000 feet per second (300 m/s) with the ​7 ¹⁄₂" "cavalry" barrel length, even though modern solid-head cases make it impossible to load a full 40 grains.
Specifications for 20th-century smokeless loads set velocity with a 255-grain (16.5 g) round-nosed flat-point bullet at 870 feet per second (270 m/s) providing 429-foot-pound-force (582 J) energy.

The version of the .45 Colt as of 2014 differs from the original cartridge case in that the rim is significantly larger (with a groove immediately above it) and the internal aspect of the primer pocket is surrounded by solid brass instead of protruding into the powder chamber.
This "solid head" case is stronger and resists deformation of the primer pocket.
Some commercial and custom revolvers and single-shot pistols (such as the Ruger Blackhawk, T/C Contender and others) employ high-pressure loads that are dangerous in the Single Action Army and other vintage arms chambered for the .45 Colt cartridge, especially 19th-century "pre-smokeless" revolvers, which should be fired (if at all) with black powder only.

Prior to World War II, the .45 Colt used a groove diameter of .454"; post-WWII production adopted the .452" groove diameter of the .45 ACP.
From 1924 through 1940, a small number of Single Actions in the pistol caliber .45 ACP were produced.
Colt's record lists several Single Actions chambered for the .45 Colt cartridge and being accompanied by an extra cylinder for the .45 ACP.
The first Colt Single Action Army prototypes were manufactured in .44 American caliber for the 1872 government trials, as the .44 American was the cartridge used in the 1,000 Smith & Wesson Model 3 revolvers issued to the troops. After the tests, the Colt was declared the superior revolver and the government specified that a .45 caliber cartridge would be required. With the adoption of the Colt Single Action Army revolver in 1873, the service cartridges were Copper-cased .45 centerfire Benét inside primed "Colt's Revolver Cartridges" loaded with 30 grains of black powder and an inside lubricated bullet of 250 grain. They were manufactured at Frankford Arsenal, Philadelphia, PA, through 1874. In 1875, the cartridge was shortened so that it would also function in the newly adopted S & W Schofield revolver. It was designated "Revolver Cartridge" and loaded with 28 grains of black powder and a bullet of 230 grain. The Bénet-primed cartridges were manufactured until 1882 and then replaced by reloadable cartridges with brass cases and external primers.
The original .45 Colt black-powder load of 40 grains propelled the 250–255 grain bullet at a nominal 970 feet per second (300 m/s). Authors John Taffin and Mike Venturino have demonstrated that modern black-powder loadings of the .45 Colt cartridge frequently achieve velocities in the vicinity of 1,000 feet per second (300 m/s) with the ​7 ¹⁄₂" "cavalry" barrel length, even though modern solid-head cases make it impossible to load a full 40 grains. Specifications for 20th-century smokeless loads set velocity with a 255-grain (16.5 g) round-nosed flat-point bullet at 870 feet per second (270 m/s) providing 429-foot-pound-force (582 J) energy.
The version of the .45 Colt as of 2014 differs from the original cartridge case in that the rim is significantly larger (with a groove immediately above it) and the internal aspect of the primer pocket is surrounded by solid brass instead of protruding into the powder chamber. This "solid head" case is stronger and resists deformation of the primer pocket. Some commercial and custom revolvers and single-shot pistols (such as the Ruger Blackhawk, T/C Contender and others) employ high-pressure loads that are dangerous in the Single Action Army and other vintage arms chambered for the .45 Colt cartridge, especially 19th-century "pre-smokeless" revolvers, which should be fired (if at all) with black powder only.
Prior to World War II, the .45 Colt used a groove diameter of .454"; post-WWII production adopted the .452" groove diameter of the .45 ACP. From 1924 through 1940, a small number of Single Actions in the pistol caliber .45 ACP were produced. Colt's record lists several Single Actions chambered for the .45 Colt cartridge and being accompanied by an extra cylinder for the .45 ACP.
Colt Single Action Army