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Old November 20, 2013, 12:38 AM   #1
chipchip
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Temperature

How much does temperature effect ballistics. Lets say 60F vs 40F or 40F vs 20F
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Old November 20, 2013, 12:58 AM   #2
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air molecules move more when hot than cold. you also have to account for how thick the air is to begin with. if your shooting range varies greatly in feet above sea level then that can affect your ballastics way more than 20 degree temp difference.
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Old November 20, 2013, 01:07 AM   #3
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Generally you will get higher velocities the warmer the temperature, which will result in change in POI. Some powders are less succeptible to temp changes while others can vary rather drastically.
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Old November 20, 2013, 06:51 AM   #4
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Example for 40° vs 20°,
When using a .22 lr, a subsonic round could become a supersonic round if its cold enough.
The speed of sound is slower in the cold, so maybe that subsonic .22 lr at 1000fps can now break the sound barrier.
This would change trajectory I imagine... Have not tried this theory out, but kind of a fun fact I picked up a while ago.
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Old November 20, 2013, 08:07 AM   #5
Bart B.
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Corrected data to match Hatcher's Notebook info

Cold powder shoots bullets out slower than hot powder. Some tests were done with the .30-06 showing for a 1 degree change in powder temperature, there's about 1 to 2 fps change in muzzle velocity. Details can be seen at:

http://books.google.ca/books?id=yESN...rature&f=false

At long range with the .30-06, there's about 1.5 to 2 MOA change in elevation on the sight for every 50 fps change in muzzle velocity. At 100 yards, the change is about 1/10th MOA.
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Last edited by Bart B.; November 20, 2013 at 08:13 PM.
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Old November 20, 2013, 08:09 PM   #6
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I won't argue with Bart, but the numbers I've seen are closer to 1 fps for each 1 degree temperature change with MOST powders. It is possible we are both right and it depends on the individual powder tested. There are powders that are formulated to be more resistant to temperature changes. They still are affected, just by a considerable less margin.

Unless you are talking about EXTREME changes it is not a huge factor for most people. If a load is developed @ 70 degrees it will be about 50 fps slower at 20 degrees. For most people, at common hunting ranges that is not a huge factor. But at EXTREME ranges, or even greater temperature changes it could make a difference.

It goes both ways. As a handloader a load I develop in the winter at 30 degrees could be safe in January, but a hot overload in August at 100+ degrees.
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Old November 20, 2013, 08:17 PM   #7
Bart B.
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jmr40, the fps change per degree these days may well be lower than what's in Hatcher's Notebook.
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Old November 20, 2013, 08:31 PM   #8
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20 degrees different will make

about as much difference as lock time, bore axis, and spin drift.

Which is to say...none to 99.99% of shooters
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Old November 20, 2013, 08:36 PM   #9
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I've read the same as Bart, 1 or 2 fps per degree but have never tested it over my chronograph. They are very clear though that air temp has little effect, it is the temp of the powder in the cartridge.
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Old November 21, 2013, 05:02 AM   #10
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jbmballistics.com has a great calculator you can change temperature, humidity, elevation and other stuff for your specific bullet weight and muzzle velocity.
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Old November 21, 2013, 09:19 AM   #11
Bart B.
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Jo6pak, how does lock time effect ballistics?

Lock time is something that happens before the primer fires. I don't see what difference it would make whether it was .001 second or 1.00 second, as long as the primer fired normally with each one.
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Old November 23, 2013, 10:45 PM   #12
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^^exactly my point
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Old November 24, 2013, 08:29 AM   #13
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Quote:
about as much difference as lock time, bore axis, and spin drift.
Lock time has zero effect on ballistics. It only affects point of aim (i.e. point of aim shifts during lock time).
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Old November 24, 2013, 10:19 AM   #14
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That's what I am saying kids.

It has NO affect on ballistics. Just like a 20 degree change in ambient temperature.
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Old November 24, 2013, 10:40 AM   #15
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Quote:
Example for 40° vs 20°,
When using a .22 lr, a subsonic round could become a supersonic round if its cold enough.
The speed of sound is slower in the cold, so maybe that subsonic .22 lr at 1000fps can now break the sound barrier.
This would change trajectory I imagine... Have not tried this theory out, but kind of a fun fact I picked up a while ago.
It would have to get down to minus 44 degrees F to make a 1000 fps bullet supersonic.
1070 fps standard velocity is supersonic when you get down to the teens. I was shooting some Remington Sub Sonics on a really cold winter day and occasionally I would hear a supersonic crack.
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