[6.5 shooter]

You would have to somehow get even cooling from muzzle to chamber so "wrapping" the barrel with tubing would not work but like one poster suggested a water jacket similar to a ww1 machine gun might work but would have to have a high volume pump and a much smaller jacket. The pump would need to move a high volume of fluid to make up for the smaller jacket diameter.( which in it's self would produce it's own heat)

You would have to pre heat or pre cool the barrel so the fluid/barrel temps were the same at the beginning and end of each shooting session.