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Temp sensitivity

 
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  #15  
Old 04-21-2013, 06:28 AM
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Join Date: Aug 2003
Location: NC, oceanfront
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Re: Temp sensitivity

While my guns will group well with various temps, none would be LR accurate over a 50deg window.
I don't know where GG got his data, or if it's valid, but the ~80deg line he mentioned is real.
Loads do seem to shift there.

It's implied that this is a bad thing(because of pressure jumps), but the truth is it's an advantage -provided you load developed above 80, and disciplined to use the barrel only within this tuned range.
After all, it's a relatively narrow range.
If I needed to, I would do the same for hunting below ~40degs, another line, where primer ignition (w/resp to capacity) shifts.

For long range shooting, there is no way I would use a single gun for a range of 40-90degs.
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  #16  
Old 04-21-2013, 08:26 AM
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Re: Temp sensitivity

Quote:
Originally Posted by Mikecr View Post
For long range shooting, there is no way I would use a single gun for a range of 40-90degs.
Two of the barrels used on my .30-.338's were fired in competition in temperatures from the upper 20's (Raton, NM, early March) to high 90's (Port Clinton, OH, late July). Both held the same load of IMR4350 and RWS 5341 primers to under 3/4 MOA at 1000. Wish I'd been able to put 'em on paper that well in the cold weather when 'twas hard to hold still shivvering like jello in an earthquake.

I've had similar experience with .308's over almost the same ambient temperature range and observed no significant difference in accuracy through 1000 yards. But the zero will change; cold air's thick and cold powder's weak so the lower muzzle velocity means more drop. Hot air has the opposite effect. Such is life.
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  #17  
Old 04-21-2013, 04:56 PM
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Join Date: Apr 2012
Location: Arizona
Posts: 44
Re: Temp sensitivity

Check out this information from Hodgon.

http://www.hodgdon.com/smokeless/extreme/page3.php#top

azsugarbear hit the nail on the head. AZ is a land of extremes both in temperature and elevation. When temps reach 90 deg. I put my selected loads in a small lunch cooler with a couple of blue ice packs or frozen water bottles when I head for the range. I put a couple of layers of bath towel material between the cartridges and the ice packs. I take out 1 cartridge at a time and only when the barrel/action has cooled to my liking. This has worked well for me. I won't test loads when temps reach 100+.
This means shooting very early and not for very long during the summer. For what it is worth it works for me. RL22 and H4831sc are my mainstays for powder in the .270 and 30 cals. Always remember that what works for one rifle may not hold true in another or at least to the same degree.
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  #18  
Old 04-22-2013, 11:54 AM
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Join Date: May 2007
Posts: 268
Re: Temp sensitivity

You also need to consider what chamber the powder is going in.
In my 300Win rifles I get better accuracy with Rl-22 and have not found it to be twitchy. I do not shoot in 120 degree weather either so keep that in mind.

If I have my facts right the military uses H1000 in the 190SMk load?
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  #19  
Old 04-22-2013, 12:09 PM
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Re: Temp sensitivity

Quote:
Originally Posted by X-man View Post
If I have my facts right the military uses H1000 in the 190SMk load?
In the .300 Win. Mag. ammo loaded by the USN's Crane Ammo Depot for sniper use I broke down had Reloader 19 powder in it and confirmed by talking with them.

I doubt any slower powder would give the consistant accuracy it does. IMR4350 under 190's and 200's HPMK bullets was the favorite back when the .300 Winnie was popular for long range prone matches.
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  #20  
Old 04-22-2013, 12:15 PM
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Location: Meridian, Idaho
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Re: Temp sensitivity

Interesting thread. One day I went out and pounded a rock at 800 yards. I had no vertical movement in the entire string. All landed with in.5 MOA. I would have to guess from chamber to fire each round was in for 30 seconds to 1 minute. I did take a break from the 1st 4 rounds and went down to check the results. Came back and shot the next 4. The barrel on this rifle gets a little warm after 6 consequetive shots so I like to give it a rest after 4.

I use retumbo which should be stable like 4831 and 4350 by Hogdon.
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  #21  
Old 04-22-2013, 12:30 PM
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Join Date: Dec 2005
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Re: Temp sensitivity

Brent, if your barrel's a good one and properly fit to the receiver, your should be able to start with a cold barrel then shoot 30 to 40 shots 20 to 30 seconds apart and not see more than about 1/4 MOA rise in bullet impact at 800 yards. If it won't do that, something's wrong; probably the way it was fit to the receiver face; a common problem.
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