I think the length and surface bearing area contribute a lot to the heat generated in a barrel - maybe as much as the powder blast itself. If you've ever gone downrange and found a bullet you've just shot in the embankment - it is smoking hot and probably not due that much to the powder blast. Also most match grade barrels are tighter at the muzzle causing even more friction and heat. I have always looked for "cooked" meat around the bullet, but the bullets I use mainly leave exit holes on the way out!! This is the reason I like bullets designed with less bearing area for their length - less friction, higher velocities with less wear and tear on the barrel. I also think having multiple bullet gas checks to prevent the gas from escaping around the bullet makes them more efficient.