Every deer I've shot with the .45-70, with either jacketed or HardCast lead, has gotten "the leaks" pretty bad.

Hawk Driver, I've used/am using that bullet, too. About evenly split with DRTs and runners, depending on where I hit them. I'm not running mine as fast as you, I generally use the Speer Unicor to go that fast, and then I go straight to 2200 fps. But that Hornady at an intermediate speed is a hammer!