Temperature Sensitivity

[Jim Hundley]

I have been loading my .300 Win. mag. cases with H-1000 because of the temp. insinsitivety of this Extreme powder. However most loads with the longer bullets are quite compressed. I was searching my Quick Load program for alternate powders that would give me the desirable case fill and the targeted velocity. IMR 7828 sc keeps popping up as an ideal candidate. My question : is IMR 7828sc a good powder for the .300 Win. mag / 180 gr. bullets and how much velocity lose can be expected from 75 degrees down to 20 degrees ? Can I figure 2 fps. per degree of temperature less than 70 degrees as a rule of thumb ? The H-1000 does not vary enough to matter, verified with the Oehler 35 in such temps. Any suggestions ?
Thank you,
Jim

 

[RockZ]

Try ramsnot magnum.
Barnes bullets did a test with the 300 win and 180gr. Bullets.
They found magnum was a bit less sensitive than H1000

 

[Gunpoor]

This has nothing to do with temp sensitivity but I found that loading heavily compressed loads of H1000 gave mixed results. By that I mean when I first loaded some compressed charges of H1000 in my 270Win they would shoot into a bug hole group and then after the loaded cartridges would set around for a month or more the accuracy would start to fall off some, and then this weekend I shot some that had been loaded around the first of the year and the accuracy was just plain horrible. I pulled the bullets on those that I had left and the powder was so hard I had to use a pick to break it up to get it out of the cases. I believe the deteriorating accuracy was due more to lack of sufficient ignition than anything else. I also tried some of the same bullets loaded with an uncompressed load of H4831SC with stunning results of both accuracy and velocity. BTW, I have heard somewhere else that the 300Win performed well with Ramshot Magnum.

 

[Derek M.]

A very reliable source has told me Ramshot Magnum is a very temp stable powder. Retumbo is also a great choice in the 300 as is 7828SC.

I personally have yet to find a reason not to use IMR powders based on temp stability. IMR, for the first 12 or so years of reloading was my first powder choice and I still keep a good 10 pounds of it on hand in 4350, 4831, and 4064.

 

[Jim Hundley]

Thanks Gunpoor and Derick,
I like H-4831sc, but I don't seem to get the velocity I want with book loads. I have exceeded book with no problems, but I am not confortable doing this even though there doesn't appear to be pressure signs. My goal is 3075 fps. with very good accuracy from my 25" Hart. The rifle will do it and I have gotten less than 1/2" groups at 3100+ fps. with H-4831sc, but again I was loading over book. Any suggestions ? Will try IMR-7828sc. Thanks for the replies !
Jim

 

[Derek M.]

A load book is published based on the test equipment used by the bullet or powder manufacturer. It is a GUIDE. If you load over book and it is safe in YOUR rifle, it doesn't matter. I do it all the time.