Rifles: How Temperature Affects Load Accuracy

Before we get to the real subject of this post, permit me to discuss life on other planets. According to informed sources, the number of these bodies in the universe is 10 to the 24th power, which reads 1,000,000,000,000,000,000,000,000. Given the immensity of this figure there is surely life of some kind out there, perhaps quite a bit of it. And no matter what form it may take, or how alien it may be to us, none of it can possibly be more horrible than Chris Matthews. Thanks for bearing with me.

One of the factors that is not given enough credit for making the life of the rifle shooter a living hell is the effect of temperature on the rate at which powder burns, and therefore on accuracy. I got a good taste of this last week when I went to the range with Old Sure Thing, my impeccably precise .30/06.

I was shooting a load which I had worked up last summer (you do remember summer?) involving a hot charge of IMR 4831. I remembered it as being very accurate, but the groups that showed up were not. Originally, it would put five rounds in .602, but a few days ago I was hard pressed to keep three shots inside 1.5 inches.

The joker was the temperature. My meticulous records showed that I had come up with this load in August, and that the temperature was in the mid '70s. On the day of the dismal groups it was 23 degrees, and that 50-degree difference was enough to screw things up royally.

There's not much you can do about this except be aware of it. There are powders that are advertised as being insensitive to temperature, and you can try those, but the best approach is to keep track of how everything shoots and what the temperature is at the time.

If this doesn't depress you sufficiently, I can point out that altitude can also do strange things to the way a rifle shoots, and you have to check that, too. It's enough to drive you to flyfishing, which at least you do in warm weather, unless you fish for steelhead, in which case you deserve whatever happens to you.