How much does the temperature affect ammo? I am shooting daily in the hills of Texas and the temps are in the 70 - 90 degree range. I am hunting in Idaho in two weeks where the temps should get into the teens, (possibly) during the nights. Is my gun going to shoot considerably different in the colder weather? Will my favorite loads still be my favorite in cold weather?
Thanks

Good question. Some folks who are more deeply into this will be along to give you a good cut on the temp issue.
The things that I know are, depending on what powder you use, pressures and velocity will increase going from colder to warmer temps, and visa versa. If you develop a load in cold weather that is near max, it "may" be an overload it hot weather.
There are powders today that are more stable than early powders, that aren't affected by temp changes like the old powder I'm familiar with. Hogdon has some powder that is supposed to better stability than others.
If you go from 90 degree temp in Texas, where you developed your load, to Idaho with temp in the teens, I would expect you would have less velocity (lower pressure) with attendant change of impact point. But, the question is, what powder are you using?
I'll let the other guys give you a more detailed answer.
Don

It depends. Loads developed in heat above 70°-80° with ANY powder will have higher pressures. Some powders are very slightly more tolerant of heat in that range. ALL powders over that range will be affected. The temperature tolerant powders are mostly tolerant of extreme cold, not of heat.

I've chronogaphed loads at home and also in the cold of Wyoming and Montana. I've lost as much as 200fps on loads (using RL22,) and still got my game. When using that propellant years ago I dropped one grain in the charge when the heat set in at home and would revert for hunting for about the same velocity in cooler weather. All you can do for the extreme cold, like near 0°, is to use one of the temp tolerant propellants put out by Hodgdon and Ramshot. I've chronographed them in extreme cold, again near 0°, and they lose no velocity from loads chronographed under 70° at home.

Best thing to do at this late stage is to sight in your gun near your hunt area. Likely it won't make much difference for shots under 200 yards. Anything over that I'd worry a bit about both accuracy and bullet drop.

I have it narrowed down to R-22 58.0 gr and IMR 7828 and 61.0 grains, shooting the Nosler Part. 160 gr. These two loads, so far have been the best. I have not pushed the "max" from the book.

Hey cashflow

Another thing to remember is that changes in altitude can make a big difference and may offset the changes because of temperature. I live in Houston and loads I develop for elk hunting in Colorado will shoot 100 fps slower in the cold but will shoot 100 fps faster because of the 8000' altitude. And both my Elk guns love RL22 which is supposed to be temperature sensitive.

Just an afterthought.
When you go to Idaho, if you can, shoot a target to see what effect the temp difference has on your load w/respect to POI & any change.
Let us know.
Good Luck on your hunt!!!
Don

Steve The chart is quite interesting. I have not had nearly the variation as shown. Even w/ Alliant powders. I certainly don't doubt it. Guess that proves the good ole theory that "Every rifle is different".

Reloader