I too found a small cannon ball or “grape” or “canister” shot as you both call it. Looking on the internet I saw it identified as grape shot, but know very little about the history of cannons, so won’t argue with anybody!
I literally stumbled over it in a field that was being prepared as a parking lot. I thought I had kicked up a geode, but when I picked it up I knew right away what it was.
There were 16 of these balls per canister, fired by a 10-lbs Napoleon gun. They were usually double loaded and had an effective range of about 400 yards. Every chest had 4 of these, 4 shrapnel, 12 shell, and 12 solid shot, 4 chests per limber, and one limber per gun.