Measurements will not help date the round ball very much, they have been used for so long and even made today in many calibers that were used 200 years ago. In general there is no accurate way to date round balls. The white oxide can and will build up at different rates depending on lead and soil composition. Folks were regularly using muzzle loaders in some areas up into the early 1900s and of course the rebirth of muzzle loading hunting that got going fifty years or so back. Musket ball implies military use, round ball is a more encompassing description for an item of which many many more were fired in hunting or target practice than were ever fired from military muskets in our country.