Dating a single musket ball, by itself is difficult at best. Some dating can be acomplished (for a very large swath of time) by determining the caliber of the ball. Small .20 to .44 caliber buckshot, and .45 to .73 caliber rifle and musket balls can be assigned a period of about 100 years, at least here in the U.S. Generally, the balls are more clearly identified as to time period by those items that are found with them. Some dating is possible by determining the method of manufacture, i.e.; were they handmade or factory produced? Hand made balls have fairly clear indications of being such. There were some very unique calibers that were not mass produced that can give close date approximations. The ubiquitous .75 caliber British �Brown Bess� can't be dated, but if balls were found mixed with, say, the .68 - .70 cal. round ball fired by a large caliber American made arms (such as the Kentucky Long Rifle) or the .52 - .53 caliber balls, which were uniquely associated with the Lancaster rifle, or full-stock Pennsylvania long rifles made by Lancaster gunsmiths like Jacob Dickert and B. D. Gill, which St. Louis newspapers advertised for sale circa 1828, then both can be relegated to a date of a few decades...Best of luck!