Shiloh Rifle Forums

Living in Florida, I don’t have the capability to test the point of impact of a load developed to shoot at 80 degrees and then shot at 10 degrees. Does the temperature affect where the bullet will strike?

Air density does have an effect on the impact point. Air density is effected by temperature (cold=higher density, hot air=lower density) But, altitude above sea level also has an effect on air density. Sea level will be most dense if comparing with the same temperature at a higher altitude. I've never seen much difference due to relative humidity. FM

VBull, I get that. Let’s increase our altitude in cold weather so air density is taken out of the equation to eliminate that variable. I can approximate air density with software such as JBM and make a good guess to those corrections beforehand

I guess that might work as long as you inform your rifle to perform as to the results from the program.

Maybe the question should have been rephrased to ask what happens to the velocity of a load developed at warm temperatures when fired at cold temperatures. Referencing JBM was an attempt to rule out all but one variable. I’m aware a ballistic program is a guide only and seldom reflects reality. So, slower, faster or same. To reduce the “sharp shooting”, velocity as measured 15’ from the muzzle

To answer your question about temperature effects on black powder, all propellants lose energy with decrease in temperature. Much of this can be attributed to what chemists call "activation energy". Activation energy is energy that must be pumped in in order to get a reaction started. Lets say that black powder starts to burn at 400 degrees F. Lets also say that a hunter hunts on two different days, one day at 90 degrees and the other day at 30 degrees. It takes more energy to ignite the propellant charge on the cold day than it does on the hot day. This is because the propellant is 60 degrees colder on the 30 degree day and this means a hotter primer to light things up as well as more feedback energy to keep the propellant burning. Usually this is demonstrated by the cold propellant burning at a slower rate than the warm propellant. All propellants exhibit changes in burning rate with changes in temperature. You can easily verify this with a chronograph. The same load will chronograph at a lower velocity on a cold day than on a hot day. You can also verify this by noting that you have to crank the sights up on a cold day as compared to a warm day. Hope this helps.
OPS

HI not sure if this answers your ? or not but i have found over the years of shooting in anywhere from 90 above to -40 or more the only change i have found is a small amount of elevation change in my sight settings no more than 5 minutes difference. I know i have also shot some of my best scores in the winter rather than the summer dont know why but that has been my experience. Hope this is of some help. Take care stay safe and warm and have fun shooting !!