The Colt Frontier or Frontier Six-Shooter was a Colt's 1873 "Model P" type revolver manufactured in .44-40 Winchester caliber instead of .45 Colt (in which configuration it was called the Single Action Army) so that it was compatible with Winchester Model 1873 ammunition.
Production began in 1877.
Colt Frontier Six-Shooter was the actual name of the Colt pistol model, and this was acid-etched on the left side of the barrel.
After 1889, the legend was roll-stamped until 1919, when the caliber designation ".44-40" was added.
Later Colt 1878 Double Action Army Models also wore this designation on the barrel when chambered in .44 WCF/.44-40 Winchester.
The Bisley 1895 Model was the final Colt to wear the Frontier Six Shooter designation.

The 44-40 was also promoted as the standard chambering for the new, hugely successful, Winchester Model 1873 rifle.
Users of the .44-40 Winchester cartridge in the Far West appreciated the convenience of being able to carry a single caliber of ammunition, which they could fire in both revolver and rifle.
The Colt Frontier Six Shooter Revolver and the Winchester Model 1873 or the Winchester Model 1892 in .44-40 WCF caliber were one of the most common combinations seen in "the Old West".
For example, the two mounted "Cowboys" at the Gunfight at the O.K. Corral were armed with this rifle and pistol combination.
.38-40 and .32-20 (.32 WCF) also qualify as "Frontier Calibers" because 1873 and 1892 Winchesters were made in these calibers,  offering the same convenience as the 44-40 (44WCF) caliber, namely using the same cartridge in both revolver and rifle.
The Colt Frontier or Frontier Six-Shooter was a Colt's 1873 "Model P" type revolver manufactured in .44-40 Winchester caliber instead of .45 Colt (in which configuration it was called the Single Action Army) so that it was compatible with Winchester Model 1873 ammunition. Production began in 1877. Colt Frontier Six-Shooter was the actual name of the Colt pistol model, and this was acid-etched on the left side of the barrel. After 1889, the legend was roll-stamped until 1919, when the caliber designation ".44-40" was added. Later Colt 1878 Double Action Army Models also wore this designation on the barrel when chambered in .44 WCF/.44-40 Winchester. The Bisley 1895 Model was the final Colt to wear the Frontier Six Shooter designation.
The 44-40 was also promoted as the standard chambering for the new, hugely successful, Winchester Model 1873 rifle. Users of the .44-40 Winchester cartridge in the Far West appreciated the convenience of being able to carry a single caliber of ammunition, which they could fire in both revolver and rifle. The Colt Frontier Six Shooter Revolver and the Winchester Model 1873 or the Winchester Model 1892 in .44-40 WCF caliber were one of the most common combinations seen in "the Old West". For example, the two mounted "Cowboys" at the Gunfight at the O.K. Corral were armed with this rifle and pistol combination. .38-40 and .32-20 (.32 WCF) also qualify as "Frontier Calibers" because 1873 and 1892 Winchesters were made in these calibers,  offering the same convenience as the 44-40 (44WCF) caliber, namely using the same cartridge in both revolver and rifle.
Colt Single Action Army