The hide is going to stretch quite a bit... its a poor medium for gauging bullet expansion. The old saying "its whats inside that counts" applies here. The displacement of blood..... that will show up on field dressing as a black, bruising, jelly for all practical purposes, is what you can gauge your impact/ expansion by.
I prefer all copper TSX bullets, because they shoot extremely well out of my guns, don't blast lead fragments all through my game, and I haven't had any that I can tell that have deflected off bone. The name of the game for me is shot placement.... and getting that bullet to the vitals I'm aiming at. I've never had one stay in a deer, and I've never had a deer do much more than half a back flip when reacting to the shot using TSX bullets. Knowing how to execute a high spine shot everytime helps tremendously of course.... its a pretty easy shot on any deer sized game from a solid rest like a tree stand rail.