They are pretty tough the new ones are pretty much a hotcor with a thicker jacket and mag tip, I've used them on a few deer 30-06 150 & 180 gr and always got exits, but the exit holes & internal damage were smaller in comparison to win power points, rem corlokts, Hornady interlocks, speer hotcor, ect, from what I've seen they dont expand as well on double lung shots as many of the other cup and core bullets do.
I'm a lung shooter so I use mostly use hotcors, win power points sierra spts, but if I had to shoot through front shoulders or take a shot at a bad angle with a cup and core I'd have more confidence in the grand slams penetrating through over the softer cup and core bullets.
I've never recoverd one to have a look at it.