I got a new Weatherby ULW in 30-06. The temp today was 2 degrees at noon but I had to try it out. I sighted it in with some Rem 150 corelocts and then moved to my reloads. I was getting 2890 fps with the Rems and when I fired the H4350 @ 61 gr I was getting 3029 fps. I worked up from 57 gr of H4350 and was getting 2875 fps at 57 gr (150 gr Hornady). I also shot some 165 Sierra HP gamekings and was getting 2912 fps with 58.5 gr H4350. There was absolutely no sign of pressure and velocities were still rising when I reached the max loads. Will these pressures change when the temperature gets warmer? I kept the reloads in the truck till I was getting ready to shoot them and the barrel was warm enough to give me heat wave problems in the scope. I shot a 1 inch group with the dang Rem 150 factory stuff and am tempted to just use them, but it grinds me no end to shoot something with something I didn't reload. I did not shoot a group with any reloads as I was just checking for pressure and veloccity. Thus I only make 2 of each load and I was just shooting 1 of each as I wanted to get my velocity readings before the dang chrony LCD screen froze.

Powder temperature matters. Barrel temperature matters much more. You have to consider both variables.

The temperature of the barrel is fairly quickly transmitted to the powder. If you strap a thermocouple to your barrel, just forward of the receiver, do all your shooting at one barrel temperature, and let cartridges sit in the chamber for about 3 minute before firing, you can ignore powder temperature... the powder will be at the temperature of the chamber.