shaman,
Yeah, you can come to some conclusions about bullet performance even if the bullet isn't recovered in the animal. In particular a small hole, with almost no peripheral tissue damage, indicates the bullet didn't expand much if at all.
But that's far rarer than most people think, and is not usually due to lower velocity except at very long ranges. Most expanding bullet open fine as long as the impact velocity is anywhere close to 2000 fps, and softpoint or plastic-tip bullets will open down to 1600-1800 fps, depending on the design.
Bullet rotation has an effect as well. That's slower at reduced muzzle velocities, but again, at ranges out to 200 yards (where 90% of big game is taken) a muzzle velocity 100-200 fps slower isn't going to have any meaningful effect.
