I have been working up a load in my .458 Win Mag (mod 70) for hogs. This year, my trip had to be moved back several months due to my daughters surgery, so will be going in early June rather than our usual Mar. trip. My concern is that the weather in S. Texas is usually well above 100 degrees in June and I developed the load in 30-40 degree weather. Should I reduce the load somewhat to compensate for the heat? I have settled on 70 grains of IMR 4198 behind a 350 Hornady jacketed round nose bullet, sparked by a cci lg. rifle primer. Anybody have any experience with extremes of heat and what they do to pressure?

just one opinion here
if the load is a truly max load you might want to reduce it a few grains.

I usually got into trouble with hot weather when I let the ammo sit in the sun and it got so hot that it almost burned your hands to pick it up...or when I put a round in a hot chamber and let it cook a minute before firing.

Keep the ammo out of the sun and be careful about loading in a hot barrel....you'll be fine.

I've always worked up my loads in the summer just for this reason. Work them up when it's 90-100 degrees and you have a slight safety buffer when it is normal fall hunting, but you don't worry about taking them to Africa when it's hot either.

The key reason I stopped trying to get that last FPS years ago. If my load isn't safe year around I don't want it.