Multi-shot loads were very common. The English often used double shot loads on the first shot, then single loads for rapid reloading after that. Accuracy suffers with double shot loads as does striking power, so it really is effective only against massed troops at short range which is typically how the British fought from about 1750 - 1850. So what Wolfe did was not a new idea. The French later adopted the double load and the colonials (that would be you
) used buck and ball from the early 1700's through the Civil War. Buck and ball would have a .64 cal ball and 3 or more buckshot in the same cartridge fired from a .69 cal. musket. The only other European country to double shot their muskets was Denmark. I haven't heard of any other countries doing it as a regular practice.
Terry