The carbine was originally a lighter, shortened weapon developed for the cavalry. Carbines were short enough to be loaded and fired from horseback but this was rarely done - a moving horse is a very unsteady platform, and once halted a soldier can load and fire more easily if dismounted, which also makes him a smaller target. The principal advantage of the carbine's length was portability. Troops could carry full length muskets comfortably enough on horseback if just riding from A to B (the practice of the original dragoons and later mounted infantry). Cavalry proper (a 'Regiment of Horse') had to ride with some agility and engage in sword-wielding melees with opposing cavalry so carrying anything long would be a dangerous encumbrance. A carbine was typically no longer than a sheathed saber, both arranged to hang with their tops clear of the rider’s elbows and bottoms clear of the horse’s legs.
This is a shortened "carbine" version of item 22-1036, the Charleville modeled after the French 1763 musket, and was widely used in the colonies and against British troops in the Revolutionary War. Bayonet not included