I would guess that the TMK would open up really quickly and more reliably than the old MK did. When doing crop damage control of deer for 15 years I got to experiment with a bunch bullets and calibers. My experience with the MK was when it expanded it killed deer like a hand grande went off in them but there were some that just penciled through. My thinking is that the little hollow point and hollow cavity under it just caved in and it acted like a round nose FMJ and went straight through. Hornady does list the Amax as a target/thin skin hunting bullet so the TMK ought to act the same. The only thing I would be concerned with is at the velocities your are talking about the bullets rpm and speed might sling the thin jacketed bullets apart. I have a buddy that has a 257 STW and the only bullets he could get to work were the mono Barnes. The cup and core bullets disintegrated around 100 yards down range with a little white/gray puff.