In my experience, many bullets tumble after impact, especially as they lose velocity with a long range hit. A faster rate of twist will help some bullets, but adventually the slower impact velocity at long range will allow the bullet to tumble. In many cases, this is not a bad feature. In my experience, when I've had an impact velocity of over 2400 FPS, the bullets have not tumbled unless they struck a heavy bone. However, after entering an animal, the velocity of the bullets slows quickly, and at the end of penetration, the bullet will sometimes reverse with the heel going thru first as the bullet is likely more aerodynamic with the mushroom bringing up the rear.