ATAC TV Firearms Blog: Sniper Rifle Ammunition Temperature
Many factors affect the flight of your bullet, as many of you know. The ATAC TV Firearms Staff put high value on anything that will affect bullet flight. A lot of shooters spend a vast amount of time and energy taking barometric pressure readings, ambient temperature readings, calculating the Coriolis effect (Spin of the earth) and Spin drift (spin of bullet), all that affect the bullet flight. But, what about the ammunition that sits out in the sun or is exposed to freezing temperatures? The most long-range shooters are always looking for ANYTHING that has an effect on bullet flight, and might be overlooking this simple issue.
Cartridge temperature is a very important factor that can affect the flame/burn time of the propellant inside your cartridge, including the velocity of a bullet exiting your barrel. You should be recording the ammo temperature when you zero your rifle. Shooters tend to document everything else, why not the cartridge temperature that can affect accuracy.
We were at the range recently and a fellow was set-up and shooting right next to me was discussing a problem that had been occurring. His rifle is shooting low for about the first hour in the morning, then after an hour or two the rifle starts shooting zero again. We asked what procedure did he use getting ready to come to the range. He thought we were a little nuts, but told me his actions prior to getting to the range. He loaded all his gear in the truck the night before to be ready to go to the range. Including his ammo. It had been a very cold night. So now he sits with all his ammo lined up on the bench in a row, getting some sun in the bright morning. In Northern Arizona, nighttime temperatures during springtime are roughly in the 40's. The cartridge temperature in the sun was 88 degrees after an hour in sun. This might make a difference? Yea! Test it for yourself and know first hand what/how these small issues can affect your shots down-range.
Does this matter to the ammunition in your magazine of the M-16 on your back? Not that much because precise shots out of a sniper rifle have to be pin-point accuracy, where it will not be noticeable in the normal range of the AR/M-16 platform.
On your next outing to the range with your sniper rifle, bring an iced cooler with 5 rounds in a waterproof container. Let another 5 rounds sit in the sun for ½ an hour or so. Then, shoot a couple of groups back to back. You will be very surprised. It might be a good idea to carry 5-10 rounds in your pocket for this very reason. Try it for yourself, and find out that IT DOES MATTER!