Bore size for military muskets was "sort of" standardized by the time of the Rev War. French bores were in the .68-.72" range; British .75-.78" pretty much. They didn't worry about making it an exact science, because round balls for military cartridges were always way undersized - so the soldier could fire many, many rounds without worrying about fouling.
A civilian with a militia piece of "musket bore" could use issued cartridges without any trouble, in most cases. Hunting guns would have an accompanying mold, as Doyle states, as accuracy was more critical, obviously, in a hunting situation than in line combat. This was especially true of rifles.
"Powder, patch, ball!"