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Powders and MV change in cold temps

 
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  #1  
Old 03-23-2011, 11:17 PM
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Join Date: Mar 2011
Location: Nazareth, PA
Posts: 2
Powders and MV change in cold temps

I recently discovered that cold temps can make radical differences in MV.
Is this specific to power choice? I have not chronoed my current loads in the colder temps sometimes encountered while hunting, and have just read a chrono can be unreliable in colder temperatures.
I am trying to establish a load for each of my rifles with specific bullets in an effort to have my Leupold VX3s customized for bullet drop compensation. My calibers range from 243 WIN to 280 REM. I have a history of retinal tears and can't risk magnum recoil and I am trying to avoid the use of a brake.
I use a lot of IMR-4350 and RL-19, but have been trying RL-22 with nice increases in MV.
I just read RL-22 is temperature sensitive.
I hunt long fields with woodlines, the distances for shots are only limited by my ethics and caliber choice, MV helps.
Temps range from 0 to 40 degrees F with an average temp of around 17 degrees in season.
Are there powders more stable in a wider range of temps that may provide similar types of MV and accuracy? Will appreciate any sound advice.
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Old 03-23-2011, 11:47 PM
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Join Date: May 2008
Location: South of Canada and North of Wyoming
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Re: Powders and MV change in cold temps

The Hodgdon extreme powders are known to be fairly temp stable and I've heard that Alliant made RL19 stale for s defense contract. Hodgdon' Super Performance is also so supposed to be temp stable. So you should have a lot of good choices.

I've never used RL22 but have read numerous reports that it and RL25 are very temp sensitive. Retumbo and H1000 are good Hodgdon extreme powders that function in the range of 22 and 25 and are known for good performance.

Does Nazareth still wrestle against Southern Lehigh?

Welcome to LRH

-Mark
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Old 03-24-2011, 06:22 AM
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Join Date: Dec 2010
Location: Central Ohio
Posts: 126
Re: Powders and MV change in cold temps

You're going to have to decide whether velocity or consistent performance in all temperatures is most important for you. If you're lucky, you may get both. For me, consistent performance would be most important. As suggested above, I'd try one of the Hodgdon "Extreme" powder or IMR 8208 XBR. The latter powder works VERY well in my 270 Winchester and might be just the thing for your 280 Remington.
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Old 03-24-2011, 09:00 AM
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Join Date: Apr 2010
Location: Allen, TX
Posts: 2,608
Re: Powders and MV change in cold temps

I compared some data a while back that I collected using RL22 and H4831sc in temps ranging from 98F to 32F.

This was from my 7mm RM Sendero with an avg MV of around 2900 fps.

As I recall, H4831sc varied by a total of about 40 fps across the entire temperature range as compared to 200 fps for RL22.

This was not a scientific study. Among other things, the powder for each string did not come from the same Lot. But, it convinced me that it's not all marketing hype and points to one of the reasons that I beleive Hodgdon Extreme powders are so popular with competitive shooters.

Having said that, there are many variables that affect your trajectory and I don't see why you wouldn't want to collect dope on your rifle under the conditions that you will hunt or compete in.

-- richard
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Old 03-24-2011, 12:03 PM
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Join Date: Feb 2009
Location: Sedalia, MO
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Re: Powders and MV change in cold temps

Schoeneck,

All powders are temperature sensitive to some degree, with some being better than others. The basic rule for IMR series powders (and most similar single based extruded powders) is roughly 1.7 fps per degree of change. That is, a 30 degree change in temp will give a change in velocity of about 50 fps. The higher the temp, the higher velocity (and pressure), the lower the temp, the lower, etc..While some of the newer powders are being improved in this regard, they all have some sensitivity to air temp, no way around that. Ball powders tend to be a bit worse in this regard, but even they are still stable enough for military usage. I don't recall the exact range they go to, but Lake City Army Ammunition plant does test firings with ammo that's held in an oven for a period of hours (24?), but I want to say it's like 140 degrees? Could be more. They also freeze it down to about 60 below zero. The ammunition has to pass at both extremes, with pressure neither rising nor falling below set limits, and velocities not deviating beyond specific ranges. Pretty tough test.
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Old 03-24-2011, 12:14 PM
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Join Date: Apr 2010
Location: Allen, TX
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Re: Powders and MV change in cold temps

Kevin,

Is it also true that:

(a) atmospheric temp as accounted for in most ballistics software does not account for the powder sensitivity (i.e. delta MV) Rather, it's about temp/pressure/drag in flight

(b) the temp sensitivity you described pertains to the temp of the powder in the cartridge at time of ignition

(c) temperature of the barrel is mostly irrelevant unless the cartridge sits in the chamber long enough to absorb the heat

??

thanks,
richard
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  #7  
Old 03-24-2011, 02:40 PM
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Join Date: Feb 2009
Location: Sedalia, MO
Posts: 1,253
Re: Powders and MV change in cold temps

Rich,

Aside from huinting in extreme temps, I think this probably comes up more often among comeptitive shooters. Usually related to cham,bering a round in a warm (or hot) barrel at 600 and having to wait due to a target malfuntion, pit problem, whatever. Teh question always comes back to "do I extract and wait, or just leave it be and take the chance?" Overblown in many cases, but there's still some validity to the concern. Nothing like breaking a clean, perfectly called "center X" and seeing it come up a "9" out the top. Tends to make us cranky.

Anyway, I thought the info might be of interest and get him headed in the right direction.
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