Bullet Flowers or Death Spiral: What Happens to a .308 Jacket Downrange

This is an interesting bit of eye candy I picked up during a long-range shooting class the other day.

It's the jacket from a 168-gr. or 175-gr. Sierra Match King bullet from a .308 Win.

I found it on the ground near a berm I had been shooting into. I'm not sure what the bullet hit to make it come apart but the spiral pattern is the result of the jacket splitting as the bullet twisted through the air at however many thousands of RPMs it was spinning.

At first I thought the splits were where the jacket had been weakened by the grooves put in it by the rifling but that's not the case. For one, the rifling is at the base of the bullet and not along the ogive or tip, so the upset wouldn't have been caused by that. Secondly, you can see the rifling on the outside of the remains of the jacket and there's no correlation between the grooves in the jackets and the tears in the copper.