I am pretty new at metal detecting and don't know much about some of the stuff that I have found. I found this yesterday and my first thought was a musket ball but I'm not sure. Hopefully someone could help me out. Thanks!
If it is close to 5/8 I think it is a .69 cal. Maybe from a buck and ball. I say this because I have been finding a few myself. Maybe the experts will chime in for you. Welcome to T-Net.
I agree that it looks like iron or steel. Lead develops a white oxide coating which although can be stained by minerals is rarely dark brown. See if a STRONG magnet attracts to it. Try to scratch it with a sharp steel object, lead is very soft and scratches deeply easily. I think it's a ball bearing.
Nit picking, 5/8 is .62 caliber, or 20 guage, which means to 20 lead balls to the pound. Looks iron or steel to me, which means if that's the case, it's not a bullet.