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Temp sensitivity

 
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  #8  
Old 04-20-2013, 07:29 AM
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Re: Temp sensitivity

I have found the temperature stable powders to work quite well. I have used Retumbo for the last three seasons from 25-75 degrees with little or no change in impact points out to 1000 yards. I hunt Wyoming in October, and Alberta in November. I have chronographed velocities over this same temperature difference and found average velocities to be within 10-20FPS. I don't trust my chronograph as much as I do actual drop testing at long range though.
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  #9  
Old 04-20-2013, 07:35 AM
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Re: Temp sensitivity

I could not get what I wanted in my .264 Win Mag with H-4831. Has anyone tested Alliant powders for temp sensitivity ? Or IMR powder ? I will have to try Retumbo thanks Greyfox.
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  #10  
Old 04-20-2013, 09:19 AM
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Re: Temp sensitivity

Quote:
Originally Posted by 1100 Remington Man View Post
Has anyone tested Alliant powders for temp sensitivity ? Or IMR powder ?
Those powder company folks probably have. Contact them then ask about it. If they have, their data's the best on actual issues.

Has anybody "testing" ammo by shooting it actually measured the temperature of the powder in the cartridge when it shoots the bullet out? I doubt it's the same as the ambient air temperature; most likely warmer in cool/cold weather. And one must shoot the chambered round within 1 second of closing the bolt on it so a warm/hot barrel doesn't heat up the case and the powder while it's in the chamber.

I doubt a 25 to 75 degree F change in powder temperature would shoot bullets close enough to the same muzzle velocity to have the same drop at 1000 yards with the same ambient temperature for both the bullet goes through. Note cold air has more density than hot air, so a bullet leaving at the same speed in each will drop more in the cold air than the hot air. And the 25 to 75 degree F powder temperature used in the same air temperature will end up with more drop at 1000 yards with the colder powder. If air and powder temperature were the same, the cold powder in cold air would cause even more bullet drop; less energy plus more dense air equals more bullet drop.
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  #11  
Old 04-20-2013, 10:13 AM
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Re: Temp sensitivity

Testing the temp of powder is probably a misnomer, as Bart B pointed out. But I suspect the relationship between the temp of a brass casing and that of the powder move together in the same direction with some strong correlation.

As long as you are consistent in measuring the temp of the brass, you have a standard against which you can record changes in velocity. Hodgden Extreme powders seem to do much better than others, but velocities still change. Here in AZ, I have found that as you move closer to the 90 -100 degree mark, the more pronounced that change becomes. I have a load for my 6.5-06 that does quite well at 50-70 degrees. But at 90 degrees, I get substantial pressure signs.

Being aware of your ammo temp and knowing how it behaves in different temps and conditions - allows you to compensate.
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  #12  
Old 04-20-2013, 12:08 PM
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Re: Temp sensitivity

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Originally Posted by azsugarbear View Post
As long as you are consistent in measuring the temp of the brass, you have a standard against which you can record changes in velocity.
How does one measure the temperature of the brass while it's in the chamber?
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  #13  
Old 04-20-2013, 12:39 PM
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Re: Temp sensitivity

Quote:
Originally Posted by FEENIX View Post
I too use the H4831SC (6.5x55, .270AI, .300 WM, .338WM) with very good success hunting in Montana's adverse weather conditions.



powder temperature sensitivity


Hopefully, GG will chime in.

Using Temperature Stable Powder - YouTube
OOPS! My bad, correction made.
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  #14  
Old 04-20-2013, 05:31 PM
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Re: Temp sensitivity

Measuring temp of brass/powder depends largely on the situation. As mentioned previously, some keep ammo on their person until it is time to shoot, while others keep it with their rifle and assume ambient temperature. Others don't make assumptions and use infrared right before putting the round into the chamber. Either way, they don't put it into the chamber until right before they shoot. Again, this probably doesn't matter much at shorter ranges, but when start stretching it out beyond 800 - 1000 yards, you ignore it at your own peril. Where I hunt, I often see swings of 50 degrees within five hours, more if in direct sunlight.
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