CDC estimates there were 30,000 death by gun shot wound in USA in 2007. If exstrapulated thru 2012 that would be a large sample to compare the validity of ballistic medium to human tissue. So you could look at the reverse logic. If the current method of ballistc testing mediium was not comparable, it would have been pointed out. The biggest point to me is that at worst you can compare different bullets to each other being shot thru the same medium So to a great extent it does not make any difference, you are comparing ballistics and bullets shot thru the same stuff.