Originally Posted by Jumpalot
I guess I'm always the exception every time someone asks this question. I've used RL22 in my 300WM in temps from over 90 to below zero. Never had a problem hitting what I was shooting at to over 600 yds. I do, however, develop my loads during summer when it's very warm outside. If you were to develop your loads when it was cold and then shoot it when it's over 90, you might run into problems. I also don't load it to max. It's then only powder I've shot in my 300. The only time I've had problems is when I was shooting on a really hot day. I blew a primer. However, this was also the lot# of powder that was later recalled by Alliant about 6-7 yrs. ago. Anyhow, it's the most accurate powder in my 300 and I've not seen the temp. sensitivity that everyone else has, so I will continue to use it. If you doubt it, don't use it as that will always be in the back of your mind when getting ready to pull the trigger.
I have read several articles on this phenomenon and had similar results with some powders
and then the next time out did not have what seamed to be a problem.
Hear is what I have seen, If you work up a load @ 70o and chronograph it if you test it at
100o the velocity will be higher with some powders but the point of impact may not move
very much (Especially at the shorter distances) at 300 or 400 yards.
If you shoot the same load @ 30o you may lose a little velocity but the POI won't change
much because the humidity is normally much less.
Also if you keep your rifle and ammo at the same temperature the spread is not as bad .But
if you leave your rifle out in the cold weather and not the ammo it will change the POI more
than if it is kept warmer than the outside temperature and the ammo is also kept in your pocket
I read somewhere that a cold rifle fireing pin may travel slower causing poor ignition and
slower velocities, Not sure about that , but I have seen actions freeze up because of to much grease and oil in the action.
The best thing to do is test the load at both high and low temperatures and note the difference
on your loading log.
I find that the Extreme powders from hodgdon do seem to help but there are other powders
that are not as temp sensitive as others so the only to find if it makes a difference is to
test you load under all conditions.
A chronograph is the only way to find if it effects velocity and shooting is the only to find out
if it changes your POI.
Not really a solid answer but the rule is "There is no rule".
J E CUSTOM