Which type? Your question is vague.
Size, materials, conditions, dirt, etc., matter.
Brass buttons ring up like shotgun casings for me here with both the ATP and ETRac.
ATP vdi = 57-63
ETRac vdi = 12/27- 12/36
Tombacs are a different arena.
TNet does have a button forum. It's hidden in the Relic Hunting Forum as a sub-forum.
GL
Peace ✌