Written by Ballistic Technician Paul Box
“I’ve heard this powder was temperature sensitive … ”
This is something I’ve heard almost daily on the 800 line. While it is true that temperature affects the burn of any powder to some degree, it is not always the reason for our accuracy going away.
So what is the reason our accuracy went sour when the temperature went down by 25 degrees?
Most powders will have what I call an “accuracy window” that it shoots well for us with a given bullet. For example, it might shoot well at 45.0 grs., 45.5 grs., 46.0 grs., and again at 46.5 grs. This is what I call a 1.5 gr. window that this rifle likes with this given powder and bullet combo. Anything higher or lower and we loose our best accuracy.
Now let’s look at the opposite end of this. We have a rifle that shoots 45.0 grs., but the accuracy goes south with a half grain increase or decrease. If the temperature changes 30 degrees with that combo, your accuracy will go too. The best accuracy window I ever had was with a 25-06 and RL-22. This rifle would shoot a 2.7 gr. spread with that powder. Needless to say, it was easy to live with.