November 20, 2013, 12:38 AM | #1 |
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Temperature
How much does temperature effect ballistics. Lets say 60F vs 40F or 40F vs 20F
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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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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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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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November 20, 2013, 08:07 AM | #5 |
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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. Last edited by Bart B.; November 20, 2013 at 08:13 PM. |
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. |
November 20, 2013, 08:17 PM | #7 |
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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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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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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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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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November 21, 2013, 09:19 AM | #11 |
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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. |
November 23, 2013, 10:45 PM | #12 |
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^^exactly my point
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November 24, 2013, 08:29 AM | #13 | |
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Quote:
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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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November 24, 2013, 10:40 AM | #15 | |
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Quote:
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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