The 2000 fps things comes from an article posted in the pistol thread discussing why rifles do so much more damage than pistols. The articles discusses how tissue cannot resist the hydrostatic shock created by impact velocities greater than about 2k fps. Below 2k fps the "temporary" wound cavity remains temporary, where above 2k, since it can't resist the tearing the temporary wound cavity stays permanent. That's the source of DLA's fixation on the 2k fps.
That's the source, but it's wrong, as is easily demonstrated with expanding low velocity bullets in hunting. Just as one example, I've had subsonic (1,000 fps) hollow points tear golf-ball sized holes through heart and lungs, with the core still punching through the far shoulder. Obviously the bullet didn't expand to the size of a golf ball, or it wouldn't have penetrated very far, but the damage was there and plainly visible when we butchered the animals. I think rost495 has seen similar effects IIRC.
I've also killed deer with both Grendel and 300 Blackout with impact velocities well under 2,000 fps, with resulting damage that was indistinguishable from a 30/30 or similar. Bullet choice matters, the oft quoted 2,000 fps mark - not so much.
Too many people look at entry and exit holes in the skin (which is very flexible) and try to draw conclusions about the internal damage; that doesn't work. Also, some of these studies about bullets needing 2000+ fps are based on very old data that does not reflect what modern bullets do on impact.
