Canister rounds were iron , not lead, and if there was canister fired in the area there would be a bunch of them around. Your ball is also small for canister. It is very difficult to determine how much diameter the lead oxide accounts for if possible at all. The lead oxide builds up but it also takes a small amount of lead off the surface to make the lead oxide. The oxide grows at different speeds in different soil conditions. A ball that has been in the ground for 100 years may have more or less oxide than one in the ground for 150 years from another area.I think you will have to accept that you have found a lead round ball of undetermined caliber that most likely dates to between 1800 and 1900. It may not be a musket ball at all, since they also used huge bore single shot pistols back in that time frame. Different countries also used many calibers that weren't standard to the U.S. and many immigrants brought their firearms of different calibers here and used them. There are many things we'll never be able to positively know about our wonderful relic finds, we just keep looking for more. Now go back and find the bowie knife the guy who lost the ball lost the same day!! Or the tomahawk the Indian dropped when that ball was fired at him but missed!!