rc, you mention lighter contour barrels will heat up faster than a bull barrel but keep in mind if we're are hunting and not planning to shoot from a bipod where weight is a plus, even a sporter barrel can be very accurate in 308.
What does barrels heating up have to do with this?
Properly built with all the right stuff, neither bolt or semiauto rifles change point of impact as their barrels heat up.
Nor does the barrel weight or profile matter. As long as they whip and wiggle the same for each shot, best accuracy is at hand; they do in both types.
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Long Range High Master
NRA Smallbore Prone Master