Looks like a musket ball. Were used from 1500's to the present. Reenactors still use them. Try putting a set of calipers on them. To tell the age, you're going to have to research what kind of site it came from. Nice going.
Comparing it with the nearby tape-measure, that lead ball appears to be about the right size (.370-to-.380-inch) to be a "cap-&-ball" .36 revolver pistol-ball... but in the first photo it seems to be out-of-round. If it really is out-of-round (slightly egg-shaped), it is not a pistol-ball.
According to te educational chart below, the largest Buckshot ball measures .36-inch. Check this ball's diameter with a Digital Caliper. If it is larger than .36, it is not a buckshot.