How temp effects load development...?

Crop Damage

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Joined
Jun 10, 2007
Messages
59
I'm tweaking a load for my 300 rum this afternoon, using 165 accubonds. Currently using IMR7828. I also have retumbo, h1000, rl22 and rl25 on hand. I'm overthinking the whole cold vs warm temp issue, I hope, but wanted to ask you all to be sure.

I'm loading ammo here in the 65 degree house, and walking right out back to shoot. The entire loaded cartridge is only exposed to the outdoor temps for 30 seconds max before it is fired. I'm keeping the others in my shirt pocket until I shoot them.

If I get a max load worked according to the book, under these conditions, will it be adversely affected in the summer, or in deer season when it stays chambered in the cold for a few hours? Would either of these other powders be better year round?
 

brentc

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Joined
Apr 3, 2009
Messages
2,525
I'm tweaking a load for my 300 rum this afternoon, using 165 accubonds. Currently using IMR7828. I also have retumbo, h1000, rl22 and rl25 on hand. I'm overthinking the whole cold vs warm temp issue, I hope, but wanted to ask you all to be sure.

I'm loading ammo here in the 65 degree house, and walking right out back to shoot. The entire loaded cartridge is only exposed to the outdoor temps for 30 seconds max before it is fired. I'm keeping the others in my shirt pocket until I shoot them.

If I get a max load worked according to the book, under these conditions, will it be adversely affected in the summer, or in deer season when it stays chambered in the cold for a few hours? Would either of these other powders be better year round?

Marketing states that H1000 and Retumbo willl yield consistent results across all temps. However, the reality is that all powders will gain or lose velocity over wide temp swings, some just change less. A lot of it comes down to the combination of components and many times lot differences. I've found H1000 and Retumbo to be pretty darn consistent in many combinations, I've also seen them on the other end of the spectrum in others. 7828 is usually pretty good, and the RLs you listed have a reputation for temp stability issues that are commonly found with double base powders, but in the right conditions they perform very well.
 

Bigeclipse

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Joined
Aug 10, 2012
Messages
1,935
I'm tweaking a load for my 300 rum this afternoon, using 165 accubonds. Currently using IMR7828. I also have retumbo, h1000, rl22 and rl25 on hand. I'm overthinking the whole cold vs warm temp issue, I hope, but wanted to ask you all to be sure.

I'm loading ammo here in the 65 degree house, and walking right out back to shoot. The entire loaded cartridge is only exposed to the outdoor temps for 30 seconds max before it is fired. I'm keeping the others in my shirt pocket until I shoot them.

If I get a max load worked according to the book, under these conditions, will it be adversely affected in the summer, or in deer season when it stays chambered in the cold for a few hours? Would either of these other powders be better year round?

Also if you find your rifles max load...and don't back off...then yes...in mid summer heat you could run into trouble. I don't think we would be talking a rifle blowing up but more likely a very sticky bolt lift or stuck case. I have not experienced this yet myself but had a similar post about this very issue and that was what I was told by members here. So...my advice would be either test in summer temps...and then varify point of impact change prior to hunting season OR develop your load in normal hunting temps and then do not shoot that load in the summer for safety reasons. I know a few people who actually developed two loads....one for summer plinking and one for hunting season.
 

4xforfun

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Joined
Oct 1, 2007
Messages
1,476
Exterior temps don't matter one iota for load development. If you keep your ammo warm, and don't let the loaded round sit in a HOT/COLD chamber you will be GTG.

Now, if you are going to USE/HUNT with the gun in cold temps, then you should let the ammo cool off during load development. Hot/cold ammo is different. The amount of difference is dependent on what powder you use.
 

Crop Damage

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Joined
Jun 10, 2007
Messages
59
Thanks, that's what I was wondering. I'll work on summer vs winter loads. Gonna leave some loaded rounds on the porch tonight and see how they shoot tomorrow. I'm 1.5 grain below book max with the 7828, that should help a little in hot weather. My rifle doesn't seem to like the retumbo so far.
 

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