temperature and accuracy

[506th]

New to reloading.

I have been reloading for my .270 over the summer. After trying many types of bullets and powder weights, I have found that 50 grains of IMR-4831 and 150 grain Nosler partitions grouped the best. 1 inch groups (3 shots) out of a cold barrel are the norm. Temperatures over the summer were high 80's and low 90's on average.

My question is if I were to go hunting when the temperature may be 20-30 degrees colder, how much could this affect my accuracy?

What about in the dead of winter where temperatures could be around 0?


thanks

[MT4XFore]

506th,  Some brands of powder and/or lines within a brand are very insensitive to ambient temperature.  Unfortunately, IMR 4831 IS NOT one of them.  Large shifts in temp does affect pressure, velocity, and therefore accuracy in loads with temperature sensitive powders.  It can be somewhat problematic if you develop a load in cold weather and then try shooting it in very hot weather, especially if that load is on the upper end of the pressure scale in cold weather.  Reverse that situation, as you have done, and you may find that in colder weather that load may not group well or even shoot to the same point of impact.  That is a problem we handloaders have had to deal with for years.  But nowdays, Hodgon has a line of "Extreme" powders that maintain their characteristics in all temps.  Other powders such and the excellent line of Ramshot powders also have a fine reputation for being very temperature stable. Maybe this will help some: http://www.hodgdon.com/smokeless/extreme/page4.php   Good luck, and God Bless.

[ricciardelli]

http://stevespages.com/tempvsvelocity.html

This is one reason to get to your hunting site a day or two before season.  Fire a couple of rounds to ensure that your bullets are going where you want them...

[Questor]

506th:

It won't affect the load much, but it can affect your rifle a lot because of the changes in humidity and any changes in altitude.  I recommend always, without exception, to test your zero just before you go into the hunting field, and to do it in conditions as close to the field as you can without spooking game.

[Redhawk1]

http://stevespages.com/tempvsvelocity.html

This is one reason to get to your hunting site a day or two before season.  Fire a couple of rounds to ensure that your bullets are going where you want them...

Sound advice.  

[Lone Wolf]

agree with what has been previously posted about IMR powder and it's temp sensitivity. A load that shoots say 2700 FPS in 90 deg weather may only shoot 2600 in 20 deg weather.

Related to shooting what may be a sub MOA load at the hotter temp may be a shotgun pattern at colder temp as it's slower speed doesn't coincide with your barrel's harmonics.

Anyway here's a test to see what your load will do at lower temps - the night before you go shooting put about 20 rounds in your freezer and keep them there overnight and the next day when you go to the range put them in a small cooler with one of those chemical packs like blue ice. Then shoot them one at a time in you rifle, being careful not to keep them in your rifle's chamber more than a few seconds. Compare your groups