Re: Sporter barrel on a tactical rifle?
Well, the deck is probably stacked against it, but it <span style="font-style: italic">is</span> possible to make a sporter weight barrel shoot well. With some attention to loads and possibly a pressure pad at the end of the barrel channel, it can also be possible to manage POI migration when the barrel gets hot.
Please note that the addition of a pressure pad will almost certainly require redeveloping the load, as harmonics are significantly altered.
Hot barrels and long strings of fire are a LOT harder on barrel throats, but honestly, they are just as hard on a heavy barrel as a lighter one, and the lighter barrel usually cools off quicker afterward. There's just no getting away from the fact that rapid fire strings are hard on barrels, and lighter weight barrels have less mass to absorb the heat, so they definitely get hotter.
My advice with the handloading is that handloading allows for downloading, and the .300WM can also be loaded like a .30-'06 or .308, and the extra room in the boiler can sometimes help ease the load on the throat. Downloading with slower powders is a nono. Stick with loads that are designed for the smaller chamberings, a rifle that shoots like a .308 or .30-'06 is definitely no handicap, and it just may make the whole process less stressful on both you and the rifle. If you can get the 155 up to Palma velocities, that's a reasonable goal.
If there's any real handicap here, it's not the barrel weight, but rather, the barrel length. Palmas like longer barrels, but that's because they are limited to the .308's case capacity. You don't have that problem, and it's quite possible you can reach your goal without resorting to a full-power .300WM load. Just make sure that when you're downloading you're doing it with powders at the faster end of the burn rate spectrum.
I'm doing something similar with a very light weight .30-'06, which can sometimes be loaded to .300WM performance levels. That's with heavy bullets and stout loads of slower powders. I choose to explore the other end of the spectrum, and sometimes we can make such things work somewhat satisfactorily as well. 150's and 165/168's shoot very nicely, and without a major recoil penalty.
Just remember, I'm just another guy with an idea or two, and that's definitely not something to bet the farm on. I'm not trying to contradict the common viewpoint, I'm simply trying to complement it. That common viewpoint has a lot better odds of being correct, I'm just not your average shooter. My Wife keeps a frypan dedicated for beating sense into my noggin...
Greg