It's not a .60-caliber ball. Pardon me please, but for the purpose of Education, I have to tell you that you are misinterpreting the .601-inch diameter measurement of your fired bullet with rifling-marks (ridges) on it.
Caliber means the diameter of a firearm's bore, without including the rifling-grooves in the bore. So, to learn the bore diameter of the rifled firearm which fired that ball, you need to measure it in-between the rifling ridges, not on top of the ridges.
Also, when measuring dug bullets, you need to account for the thickness of the lead-oxide "patina" on the bullet.
So, taking into account the height of the rifling ridges and the lead-oxide patina on your fired lead bullet/ball, the .601" diameter measurement you got from measuring it across its ridged sides means it was fired from a .58-caliber rifled firearm.
I realize the explanation above is rather "technical," especially for readers who are not familiar with terms like "bore-diameter" and the depth of rifling-grooves. I hope I've made the explanation clear enough. If not, let me know, and ask whatever other questions you need to.