I'm not sure that's a bullet. What is the dark brown? The outside doesn't look lead to me.
I may be seeing things wrong, but when I blow the pics up it looks like a sandstone looking material. I've just never seen lead that looks like that. It doesn't have that white or gray look.
Maybe, it is and I've just never seen bullets come out of the ground from VA..That could be too.... and....I don't have a better ID.
I've found a few of those. It's a gall stone. People used to go out into the back yard to pass them so they wouldn't scare the kids with all that screaming.
I have an AT Gold and it really hits hard on lead, too. Looking at the numbers scale in the manual (page 21), 71 is in the upper part of the lead projectiles zone. That must be really old with that thick of crust.