Hi! Just joined and saw your bullet. It is a Civil War vintage 58 caliber minie ball. It looks like it was molded at the Springfield Arsenal in Massachusetts. Most of them were. You can tell by the way the rings look.
Fyi.. I have been hunting civil war stuff off and on for about 50 years.. My first year of hunting I got into a trench in front of Ft. Hell (Ft. Sedgewick) down in Petersburg VA. Found ten cases of minie balls, 10,000 rounds, stacked up and left behind when the troops moved out. AHH!!!! was a grand day!!!!