When developing a new load at 35 ft above sea level and 80% humidity with 80-90 degree temps, will this affect my pressures and how will it affect this load come fall temps when it get down to the 50's or 30's.

I use H-4831SC and IMR-7828. It seemed to me that I was reaching higher pressures before I should have and was wondering if location and temperature had anything to do with this.

Temperature will raise pressure, humidity will lower it, but the temp will have the greater effect. Your pressures should be lower in the fall, I like to work loads up when it's 90-100, leaves a margin for hunting season, and you know it's OK for Africa.

Thank you.

I do most of my load work up in Tucson's summer. Not much fun when it's 110 in the shade but loads later in the year are safe. However, I do check them out come cooler temperatures prior to hunting. I haven't seen enough change in velocity to be worth bothering with but then, it doesn't get all that cold come hunting seasons here, most of the time anyway.
Paul B.

Don't forget, air temperature does NOT affect external ballistics. The temp of the powder does. It's an old Benchrester's trick to keep their cartridges at a uniform temperature and to not chamber them until just before jerking the trigger. It's not as easy to do that when hunting but if you put your mind to it you can come up with a solution that is workable, most of the time.

Humidity does affect external ballistics but not to the extent that most guys think. Altitude and the ability to accurately estimate the wind and yardgae will cover up any errors due to humidity.

There are good external ballistic programs available free. You can input all of the different factors and see for yourself what happens.

JMHO

Ray

Ambient temperature is not as big a factor as some believe.....but the temps that can occurr by letting the brass ammo set in the sun can cause them to be extrtemely hot...or putting rounds in a very hot chamber and let them assume extremely high temps can be very bad. I picked up rounds in my truck that had been sun baked and they was so hot I couldn't hold them in my hands.....

I think this happens much more in hot summer days but I wouldn't be at all concerned about a mere 60 degrees difference in temps

Ambient temp can affect pressure and velocities in my experiance. I ran a test on temp effects useing R22 in a 6.5x55 and reported on it here a while ago.
http://www.24hourcampfire.com/ubbthreads/ubbthreads.php...rch=true#Post1460421
The ammo in these tests was shaded until fireing, and the barrel was allowed to cool 2-3 minutes between shots to help prevent it from causing variations not related to the outdoor temps present that day.
In this instant I found about 10% difference in pressures, whether or not other powders act similar or not I don`t know. The chances are though they will show some variation IMO. Take note also the velocity only changed 10 fps with the rise in pressure. It makes one wonder as to the accuracy of comparing velocities to judge pressure............
For a pic of the set up I used try here.
http://i34.photobucket.com/albums/d149/1Savage/DSC00271.jpg