I doubt there will be much difference in accuracy......the real difference will be with weight......laminate will be heavier.......the bull barrel is thought to be more accurate because it's stiffer and heavier.......I'm not sure that the bull barrel is more accurate, but it heats up slower so it can be shot more without cooling the barrel.
That said, I've never shot the barrel hot on my 93 BVSS which has the heavy barrel. My buddy has the sporter weight and it doesn't seem to get hot either........I'm not sure there is a real advantage to a heavy barrel in the HMR but I like mine.....
As for ammo, my gun shoot the Hornidy 17 grain vmax the best.....federal shoots about the same.......the CCI isn't quite as good, but still not bad.....