There are theories that a bullet that is spinning faster than it needs to, maintains better stability & straight line penetration after striking bone or tissue that disrupts it's jacket and causes expansion.
We know the opposite is true from our own moose hunts here, where round ball twist muzzle loaders, shooting elongated bullets gave very poor performance on moose, the bullets rarely if ever traveling in a straight line after impact. They would even turn 90 degrees on striking a rib - yet on target, were able to shoot some amazing groups, even at 100yards.
-------------------- Daryl
"a gun without hammers is like a Spaniel without ears" King George V