I live in Houston, Texas and all my load developement is done in generally in 90 plus degree weather. How is this going to effect my ballistics when I hunt in say 40 degree weather and below.

I imagine my pressures will drop and if so, will that not effect my velocities?

Certain powders are less sensitive than others, H-1000 is supposed to be very close at high and low temps.

There is some drop but the mathematical predictions are based on absolute zero (0° Kelvin) as the starting point not zero degrees C or F.

P= pressure
V= Volume
n= moles of gas
R= gas constant
T= Temperature

All these units are metric units
In your case the pressure varies
and the temperature varies
everything else is constant.
Now this does not answer your question directly but the percent change will give you some insight into the velocity reduction.


PV=nRT

Several years ago was told by an excellent long range shooter who had done a lot of research on the temperature issue, informed us that it had been found that a difference of 15 deg. in temp. could have as much as minute of angle change in the bullet flight!! Match begins at 9am w/ temp's in the 60's and by noon the temp may well be 90 or more That 1moa variance/15 degrees seems a bit on the extreme side, but most long range match shooters will keep their ammo covered w/ towel, lid, etc. during the long string of 60 or more rounds to help prevent the ammo from being heated any more than necessary.
My preferred powder at that time was 4064 in 308
and it does not have a wide tolerance for heat and could see a difference in POI as the day warmed. Switched to Varget and it is reported that it has the least temperature sensitivity??
Does all of this have much impact on ammo for hunting purposes?? From a practical viewpoint, doubt it. Put some in the frige, leave some out in the sun for a bit and see if there is a difference would be one way to do it. I have done it and there is a visible difference in performance.

I loaded the opposite way around for my 338-378 Wby. I developed the load during the cooler months. When I shot it when it was 108 outside the increase in speed was close to 100 fps max and about 50 - 75 nominal. I would be assuming but I would think that developing a load the opposite way around I would expect a similar decrease.

Ken....

I load mostly H-4831sc and H-1000 and in the higher temps not been effected much. When I started loading my STW I was using IMR7828 and had a great shooting load in 80 degrees, the next weekend at 95 plus I had a sticky bolt and ejection issues. I have not chronnoed my loads in cooler temps yet but will try this winter.

I guess that I will just need to check my zero in colder temps. Just didn't want to take a chronny each time i went hunting to see how much I needed to change ballistic table.

The Hodgdon Extreme powders are said by the manufacturer to be less sensitive to temperature variances than any other powder out there. I use H4831SC and I like it.

Hey Harold

When loading for Elk huntin I always felt that the diffence in velocity attributable to temperature would be offset by the difference in ballistics attributable to elevation. Even though the muzzle velocity may be less for a load developed at 90* in Houston, the drop would be less at 7500' + elevation difference.

A 180 gr bullet from a 300 win mag zeroed at 200 yds, elevation difference

temperature / muzzle velocity / elevation / drop at 400 / drop at 500
90* / 3100 / 200' / 17" / 34"
40* / 3000 / 7500' / 17.5" / 34.7"

If you're just going to hunt somewhere in Texas when it's 40* outside then there may be cause for worry if you're shooting at 400 yards + though.

A 180 gr bullet from a 300 win mag zeroed at 200 yds, constant elevation at 200'

temperature / muzzle velocity / drop at 400 / drop at 500
90* / 3100 fps / -17" / -34"
40* / 3000 fps / -19" / -38"

I kinda doubt you would get much more velocity drop than that.