After the war Oliver Winchester continued to exercise control of the company, renaming it the Winchester Repeating Arms Company, and had the basic design of the Henry rifle completely modified and improved to become the first Winchester rifle, the Model 1866, which fired the same .44 caliber rimfire cartridges as the Henry but had an improved magazine (with the addition of a loading gate on the right side of the receiver, invented by Winchester employee Nelson King) and, for the first time, a wooden forearm. The Henry and the 1866 Winchester shared a unique double firing pin which struck the head of the rimfire cartridge in two places when the weapon was fired, increasing the chances that the fulminate in the hollow rim would ignite the 28 or so grains of black powder inside the case.

The Winchester rifle was famous for its rugged construction and lever-action mechanism that allowed the rifleman to fire a number of shots before having to reload: hence the term, "repeating rifle."

Note: The original 1866 was only available in the rimfire .44 Henry