>>518593853 (OP)
ER doc in a regional trauma center here.
Every GSW is different, and the only surefire way to know the caliber of the bullet is to retrieve it from the victim or measure it on XR.
In general it is often hard to differentiate entrance and exit wounds and especially so ones which strike at supersonic speeds as they, assuming they miss the rocks in your body, travel in a relatively straight line and maintain a ballistic trajectory through the victim.
Large exit wounds are the product of small arms ammunition that loses velocity and tumbles in the body often exiting sideface, or hollow-point which turn into shrapnel, but with that you dont get a large exit wound, if you get one, but many small ones.
As far as super bones. Your bones are basically fucking rocks and unless its supersonic at impact the bone is gonna fragment the bullet, yes the bone with break, but it is very rare to see a clean hole through bone without seeing scattered shrapnel. In fact the only time i can ever think of a clean through and through to bone with a bullet wad in a 15 y/o that got shot in just below the knee and the bullet went straight through the proximal tibia growth plate which is cartilaginous bone.
So, in short, OP eatches to much tv and movies and needs to go volunteer at his local ER.