I find alot of the old coppers are around 6-8 but have found some as shallow as 2. My deepest coin was an injun that was about 11-12. I also have pulled plenty old cans well over 12 more like 18-20 It's kinda a tricky sound because they are so deep they sound so much smaller and nicer like a coin when they are that depth. Ya always gotta dig those hits though because you never know when there's a nice cache waiting there for you!!!
HH,
-Evan