The reason I am asking is because I'm setting up a 308 for deer, long range groundhog, and med to long range target and I'm ordering a custom dial on a leupold scope and was wondering what temp to give them for my custom dial. I live in pa and during deer season it can be anywhere from 0 to 45 degrees and groundhog hunting anywhere from 50 to 90 degrees.
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How much does the temperature impact accuracy
- Thread starter bungiex88
- Start date
It effects the bullets muzzle velocity, which effects trajectory. I'd give them the temp that you chronographed the load and call it good. Most of the time the difference doesn't really show up until you are below 0, or above 100 and shooting at 500 yards or farther.
Most powders will see 1-2 fps difference for each degree of temp change. If you develop a load at 60* it will be 60-100 fps slower at 0*, about 40-50 fps faster at 100*.
If you choose one of the temperature resistant powders you can reduce that by at least half.
Most powders will see 1-2 fps difference for each degree of temp change. If you develop a load at 60* it will be 60-100 fps slower at 0*, about 40-50 fps faster at 100*.
If you choose one of the temperature resistant powders you can reduce that by at least half.
Here is a pretty good article of a guy who actually did a test:
http://www.rifleshootermag.com/accuracy-tests/fact-fiction-gunpowder-temperature-sensitivity/
jmr40: I agree with your first statement but wonder if velocity is changing are not the barrel harmonics also? And if they are that can cause a point of impact change.
http://www.rifleshootermag.com/accuracy-tests/fact-fiction-gunpowder-temperature-sensitivity/
jmr40: I agree with your first statement but wonder if velocity is changing are not the barrel harmonics also? And if they are that can cause a point of impact change.
603Country
New member
I assume that the OP reloads. If so, a factor to consider would be the sensitivity of the powder to temp changes. That would affect MV and POI at distance, though at 100 or so it wouldn't matter much.
And, years ago I was using IMR 4831 in my 270, and had picked the load in cold weather shooting. July rolled around and I went to the range, only to find that the load was way too hot.
And, years ago I was using IMR 4831 in my 270, and had picked the load in cold weather shooting. July rolled around and I went to the range, only to find that the load was way too hot.
mr40: I agree with your first statement but wonder if velocity is changing are not the barrel harmonics also? And if they are that can cause a point of impact change.
I suppose that is quite possible, I'm just not aware of any research into the possibility. I've seen some chronograph data showing velocity and trajectory change with extreme temperature swings. But nothing about other POI changes.
Simply a guess, but I'd think it would be more common in some rifles than others. I've seen some rifles that shoot just about anything I load in them to the same POI with predictable differences between bullet weights and speed. Others shoot to very different POI with minor changes in bullet weight or speed.
Some powders are more temp sensitive than others. I've learned that my go to .308 powder W748 does need some slight charge adjustments based upon ambient temps. For example per my data my 2 loads for my 168 SMK bullet is 41.9 in the hotter months , and 42.2 in the cooler months. Same goes for H1000 for shooting my .300 win mag using 208 Amax's i'll load 76 grains in the cooler months, and 75 in the hotter months to keep the velocities close. Many shooters don't want to have to deal with ambient air charge variables but it doesn't bother me. I've got my chrono data and it's taught me how to properly adjust charges to compensate for variables.
I live in pa and during deer season it can be anywhere from 0 to 45 degrees and groundhog hunting anywhere from 50 to 90 degrees.
What's the typical and max range encountered for each (deer/GH) application?
Trying to smack a groundhog at 600 yards would obviously require greater precision than vitals on a whitetail at 100.
I'd use "most typical" unless there is no such thing- then I'd use fifty degrees for the turret and a ballistic app to make adjustments in the field as needed. You've got ambient temp affecting bullet drop, and velocity variations determined by the powder you're using. You use the same bullet/load for groundhogs as you do for whitetail?
oldmanFCSA
New member
Temperature affects the Nut behind the gun more than the gun or ammo itself.
There is now some ammunition on the market that is supposed to be virtually independent of temperature. That takes out the variation due to powder.
Then all you need to do is correct for the effect of temperature on the ballistic coefficient of the bullet. Here's one formula to correct the ballistic coefficient for temperature. Take the current temperature in degrees Fahrenheit plus 459.4 over 518.4 and then multiply that value times the ballistic coefficient of the bullet measured at standard temperature (70 degrees).
Then all you need to do is correct for the effect of temperature on the ballistic coefficient of the bullet. Here's one formula to correct the ballistic coefficient for temperature. Take the current temperature in degrees Fahrenheit plus 459.4 over 518.4 and then multiply that value times the ballistic coefficient of the bullet measured at standard temperature (70 degrees).