Having just finished watching Jurassic Park, it recalled a discussion I had with a Friend about what to use to kill a T-Rex. Trivial wounding, for obvious reasons, would not be likely to even slow the animal down. I figure that one should probably treat it such as one would treat an Elephant hunt and take a similar firearm. As such, I think I would take a .416 of some sort(likely a Rigby...but maybe a Wby too...) loaded with solids, and a .338 RUM or .340 loaded with X-bullets for the smaller ones.