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Effects of Temperature on Velocity...

 
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Old 04-20-2009, 05:29 PM
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Join Date: Mar 2008
Location: Puyallup, Wa
Posts: 53
Effects of Temperature on Velocity...

Did a little experiment this weekend by freezing a five rounds of ammo and comparing the velocity with that of ambient temperature (55*) ammo and found:

-frozen ammo kept on ice (frozen blueberries) moved at an average of 2721fps

-Ambient temperature ammo moved at an average of 2732fps.

The load is a .308 win using lapua brass, F210 primers, 43.7 grs of IMR 4064 under a 168gr SMK seated about .005 off the rifling.

Has anybody had similar results with about 20* difference? Or should I clock the ammo when it warms up to about 80* and see where we're at?

Just looking for other views on my results.

EH
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Old 04-20-2009, 05:37 PM
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Re: Effects of Temperature on Velocity...

A few years back I developed a load for my .300 RUM at 65* using Retumbo powder. Clocked it at 3225 fps through my PVM-22 infrared chrono.

Took the rifle to Alberta with the same load and drug the chrono along. Hovering around 0*, the first one through the chrono was 3221 fps. Rifle and ammo was outside all night. I figured that was about as temperature stable as you can get.
I quit worrying about that particular combination.
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Old 04-22-2009, 01:32 PM
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Re: Effects of Temperature on Velocity...

Does anybody adjust their charge weights in accordance with the temperature in order to maintain bullet speed?

Trying to get ideas of what to look for in future experiments.

EH
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Old 04-22-2009, 02:23 PM
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Join Date: Oct 2005
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Re: Effects of Temperature on Velocity...

Quote:
Originally Posted by BENNYBOOBOO View Post
Does anybody adjust their charge weights in accordance with the temperature in order to maintain bullet speed?

Trying to get ideas of what to look for in future experiments.

EH

I've seen greater variation from 80-120 degrees than for changes below 80degrees.

However, in cold temps (around freezing and lower), some powders don't like to ignite very well and can require a magnum primer, or even a change to a different powder. An example of this is Varget, which I've had great luck with unless it was very cold (300 WSM was the cartridge).

Another example is the drastic changes that cold weather can have on reduced loads. I used to do a lot of Cowboy Action Shooting and used .357's with extremely reduced loads (Clays, Solo 1000, VV N320 etc. powders). I used an extra .2gr in loads that where intended to be used in freezing weather, because of hang fires and dud's. With a little more powder, I never had the problem. I was using around 3gr of powder behind 125gr bullets.

I've seen the same thing with reduced loads in Shotgun loads.



AJ
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  #5  
Old 04-22-2009, 02:30 PM
JEREMY logan
 
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Re: Effects of Temperature on Velocity...

One year i sighted in my 300rum at (just guessing) 40 degrees. I gathered data starting @ 300 yrds and stopped at 830. Once i had my elevation adjustments written down i could bust a 20 ounce mtn dew bottle at 400 yrds not great but not easy either at 640 yrds i could make dust fly off of a 9'' size rock . Summer came and a friend of mine said he had permission from a farmer to thin out the deer herd because of crop damage, he barely had to twist my arm , i said okay lets go i had my come ups all written down with me i used the same range finder ( leicia 1200 yrd )to range a doe it said 604 yrds same load and bullet the field was a soy bean field the plants were very small so it left alot of dust to see bullet impacts i dialed in for 640 yrds I pulled the trigger and dust flew LOW before the deer i thought what happened? Turned out it was very hot and hummid long story but i believe temp, humidity, elevation all make a big difference ......

Last edited by JEREMY logan; 04-22-2009 at 02:47 PM.
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