Re: Temperature and humidity factor - how do they affect my loads?
So, what I now deduce is that temperature affects both external ballistics and powder behaviour. Just a few days ago, it was 25C (77F) here in the evening. I shot some loads of 270WSm using Hornady 140gr, behind 59gr of IMR 4831. Grouping was 1.25" and velocity averaged 3175 fps. Yet the IMR manual states a velocity of 3081 fps for a 60.5 gr load of this same powder. My loads clocked nearly 100 fps faster with 1.5 grain less powder. This must be the obvious results of this temperature differential that we speak of. One would seemingly be quite impressed about the gain in velocity, however there must also be a gain in pressure which could be a concern, although my spent casings showed no such signs. I think that from what I'm reading is that likely the idea to keep the loads and barrels as close to hunting season conditions as possible is likely the way to go. Keep in mind, I frequent this site for the great deal of reloading information to be learned, but I am by no means a "real" long range hunter. I shoot big game to 400-500 yds, that's it. I'll likely be huntig anteloppe in September when it's still pretty warm and need to work up my loads now, not a week before season opens.
Life is short, hunt hard.