RE: .308
Heavier bullets require faster twist rates to stabilize.
Too slow of a twist will result in yawing and pitching during flight, and will be manifested as poor groupings and keyhole shaped tears.
Lighter bullets need a slower twist rate.
Too fast and the bullets will weaken, deform,or get torn apart, sometimes resulting in core/jacket separation in flight if the mismatch is extreme.
I rememberthe relationshipwith a bowling analogy...
You have to put a lot of spin on the heavier balls to get themhooking where you want them consistently. Although we aren't trying to 'hook' bullets, I've never forgotten which way it works.
Having never reloaded or competed with a 308, I can't say I know which rate is optimum for the different weights available in the caliber.