Originally Posted by MontanaRifleman
Good input, but what I'm really after is folks opinions and experience on whether or not heavy barrels cool faster than light barrels? Any thoughts on that?
I'll give this a little more thought based on some simplified mathematical analysis. I can state right now that as barrel diameter increases, steel barrel volume/mass increases to the 2nd power of barrel diameter (a squared function). Whereas exterior barrel surface area only increases to the 1st power - in other words a direct 1:1 increase of surface area due to increasing barrel diameter. So increasing barrel diameter will increase the mass of steel in the barrel at a greater rate than it will increase exterior surface area.
I'll update this post when I have some more time on my hands. But I think the increased cooling rate is minimal. The greatest advantage, with respect to heat up and cool off the larger diameter barrel has over the smaller diameter barrel is the larger barrel will take more shots to reach an equal temperature during the initial shot string, because of the greater thermal mass (heat sink effect) of the extra steel in the heavier barrel. And for the initial repetitive-fire shot string, a barrel that heats up more slowly will be less prone to warp or shift points of impact, compared to the thin-walled tubes.
There are, of course, other advantages to the heavier barrel, such as the additional mass results in less shifting of POA during the firing process. It takes more force to initiate motion of the larger mass than the smaller mass. But you've focused on rates of heat-up, cool-off, and even more specifically, heavy barrel versus light barrel temperatures under steady, methodical, sustained rate of fire. I believe that is really what you've focused on. For a given, sustained rate of fire over extended periods of time (like 2 hours), will the heavier profile barrel reach a higher or lower temperature than a lighter profile barrel.
My current perspective is this: the benefit of the heavier barrel under such sustained fire is substantially less than the benefit of the slowed rate of heat-up during the first string of firing.