Carbines are a phase between long pistols and muskets, and they are used ONLY by the cavalry.
The reason for this is that are easier to be used from the saddle, than muskets, they are shorted and also easier to be reloaded this way.
Another difference is that horseman can hold and fire carbine with only one hand, what is impossible with a musket.
This might be quite usefull during the battle, as riders have to operate their horses or might need to use another weapon at the same time.
