A couple of things from what I have read....
The 30 foot level of a mine shaft is 30 feet down from the
surface. Not the 30th level. Also.. The number of shot and
size of the shot should pretty well determine the shotgun
caliber. The spread of the shot at the skin surface should
also give an approximation of the distance between the
subject and the muzzle. The distance of penetration for
the shot should also provide whether the shell was standard
or magnum load. None of this is hard and clearly defined, but
should get in the ballpark. Also... there are still mine shafts
in the desert which have not been discovered. Just my thots..