Hay Steve,
I would say that musket ball is 150 years old, at least. Judging form it,
I would say more like 200 years old.
It takes over 150 years to get a covering like that around here.
Here is a photo. There are lead balls from World War I artillary rounds
that I dug on the right. They are made just like musket balls. But in
the 90 odd years they have been in the ground, there was little white
covering. Also, what covering was there, wore off easily after they were
dug.
On the left is a Civil War mini ball and two old musket balls. Out of
stupidity, I scraped the musket balls some. (never again) But you can
still see that some of the white covering is still there.
The ones on the left are deffinitely older than the 1900's and yours
looks like it may be even older.
Maybe that will help.
I am not an expert, but it sure looks old to me.
Happy Hunting,
Tabdog