The problem with that table is each loss rate is typically applicable to just one cartridge and bullet weight combination and can be different in another. Varget, for example, does fairly well in .308 but no better than a lot of other powders in .223. Road Clam's description of 748 is another example of how this can change.
Denton Bramwell had a good article on temperature sensitivity in the now-defunct Varmint Hunter magazine. RSI keeps a copy up, so
you can read it here. The issue turns out to be that barrel/chamber temperature has more effect than ambient temperature, and barrel temperatures can get well outside the stabilized temperature range. So the temperature compensation can work very well in a cold barrel, which is what most stalking hunters are interested in, but a varmint hunter running a string may be disappointed. if you are running a string of follow-up shots they had better be at a rapid enough pace that heat can't affect the primer or the powder much before you get to fire them. Don't let a cartridge sit in a warm chamber for long. How long you may do this will depend on the powder, bullet and the physical size of the cartridge, with powder in larger cartridges taking longer to get warm, though the primers in all of them can heat pretty rapidly and they have temperature sensitivity, too.
Another factor is that powder grain design can affect sensitivity to both temperature and pressure. 25 years ago, Dave Milosovich published an experiment in the Precision Shooting Reloading Guide in which he loaded 180 grain bullets in the .308 Winchester to specific velocities using IMR4895 and IMR4064. The grain geometries of those two powders are different, but the chemistries are the same so they have the same total energy content per grain of weight, which is important to the experiment's comparison. The 2200 fps load needed more 4895 than 4064, making it look like the 4064 was the faster burning powder. At 2300 fps the difference shrank. At 2400 fps the charge weights were the same. At 2500 fps the 4895 charge was smaller as if the burn rates had reversed. But there is another way to look at it. That is simply that the number of feet per second gained with each grain of powder was lower for 4064 because its burn rate is faster at lower temperatures and pressure (bigger perforations in the grains) but it changes less with increased temperature and pressure. In effect, it is less temperature sensitive just because of the geometry of the grain. This was demonstrated during the Irag war. The old M118LR load using a military version (flash suppressant added) of Reloader 15 was known to develop pressure problems in the desert heat. When Federal developed the Mk.316 mod.0 round for the M24 sniper system, even though they were owned by ATK who also owned RE15 maker Alliant at the time, they went with special flash-suppressed IMR4064 because it got them out of that problem. I think this explains why many have preferred 4064 in the past for target loads.
Varget was originally designed to compete with IMR4064. If you look at different loads of it in Hodgdon's data you will find with some it produces even less change in fps/grain between the starting load and maximum load than 4064 does. However, that also means you sometimes can't use enough to get to hit certain velocities at certain load densities in some cartridge and bullet combinations, which is, I believe, why some people can't seem to find a great load with it while others find it to be the cat's meow. There are trade-offs in everything.
So, back to finding a good 300 Win Mag load. If you are hunting in a manner that means you will shoot your main shot from a cold barrel, then all the temperature compensated powders should help you. The experiment with chilled rounds is a good one as long as the barrel isn't hot when you chamber them. Note that primer energy can drop in the cold so you may not get identical performance from your warm and cold ambient loads, but it should be at least good. Ice will do just fine if you are not expecting to shoot at below freezing temperatures. You can buy PCM in containers for ice cream dispensing boxes that freeze at
-6°F, +3°F, and +10°F. Unless you have a special cold freezer you would likely have to use dry ice (-109°F) to freeze both, then remove them from the dry ice and leave them out until the temperature rises to the thaw point and stalls (have started to thaw), then put them in an insulated box with the cartridges.
Let your barrel cool completely between shots. Some long-range Benchrest shooters (I'm using the capital B to distinguish the sport of printing really tiny groups from merely shooting any gun off bags on a bench) have small blowers they use to speed up barrel cooling. The better of these are basically the little battery-operated squirrel cage blowers (higher head pressure than most pancake fans) funneled into the breech to blow cooling air through the bore). My own approach, though, is to clean after every shot with a water-based bore cleaner. I pull the bolt and pump spray Bore Tech Eliminators into the chamber with the muzzle down and watch it run down to the muzzle, patch it, then pump again and let it sit five minutes, then run a wet patch followed by two dry ones. I find that and the time it takes does the job of cooling after a single shot fairly well. I figure a hunting load is likely to be fired from a clean, cold barrel, so I want to know where that combination prints.
