Help me solve this 338 Lapua Magnum problem

fireguyty

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Jul 24, 2010
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Ok, so before I get to my problem, let me explain my reloading process. When I reload for a new caliber I like to shoot all the powders that I have for any given bullet weight at 2 grains below the published max. This way I can see the best combination of accuracy and speed out of all the powders that I have before I go to the next step of refinement. I fire these in round robin style to equally distribute any variances (barrel fouling, heat, etc).

In this case I have a new Desert Tactical Arms SRS in .338 Lapua Magnum. Loading 300 grain Lapua scenars with new Hornady brass and Remington 9 1/2 M primers. I fired the following powders round robin @ 100 yards in this order:
Winchester Supreme 780
Reloader 25
Hogdon H1000
IMR 7828
Hogdon Retumbo

Grouping went as follows starting at the 2nd bullet:
S 780 two shots 1.5"
RL 25 two shots .6"
H1000 two shots .9"
IMR 7828 two shots 1.7"
Retumbo two shots 1.7"

Starting with the 3rd bullet each 3rd shot was significantly high at somewhere between 4-5 inches and was generally in the same spot for three of the powders, and the same 4-5 inches off for the other two, but high and left.

After the third shot with the H1000 I started to expect something was wrong and looked through the barrel to find a lot of fouling.

My theory is that one of the 5 powders is very dirty and started to affect my accuracy somewhere between the 2nd shot with the H1000 and the 2nd shot of Retumbo. Are any of these powders extremely dirty?

I have done this method of powder testing on at least 6 different rifles in my first stage of load development. Is this a bad idea?

Any help would be appreciated.

Ty
 

Dogtown

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Jun 21, 2007
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Re: Help me solve this 338 Lapua Magnum problem

I've used RL25 quite a bit in my SRS and I've noticed that the groups will open up after about 35-50 rounds. Retumbo doesn't seem to have that problem.