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Old August 28, 2011, 02:27 PM   #1
Join Date: February 14, 2011
Posts: 19
Casing weight tolerances?

Just started my first batch of .204 ammo, fired some test rounds yesterday with the best group at 1/4moa, second best at about 1/3moa with charges being 25.6gn RL-15 and 27.3gn RL-15 respectivley. All brass used for the test rounds was the same weight. Now heres the question, how much tolerance in weight from shell to shell should be allowed for reloading say 100 or 200 rounds (have 100 to do right now)? I weighed 20 casings, with an average of 102.28gn and a standard deviation of .90. I allowed a tolerance of +- 1gn within the average to sort my brass. These loads are not competition loads and should shoot about 1/2 moa. Is this close enough, or should I sort casings within .5 or .1 gn?
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Old August 28, 2011, 03:14 PM   #2
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Cartridge brass density is 8.53 gm/cc, according to Matweb. That means 0.853 grains, in identically trimmed and primer pocket uniformed cases, will represent 0.1 grains difference in powder space. Since pressure goes up exponentially with increase in powder charge, this is about like a 0.05 grain charge difference. Not usually a significant error. If you charge cases ±0.1 grains, then figure cases ±1.7 grains are roughly equivalent to that.
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Old August 28, 2011, 08:13 PM   #3
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Sort new brass by .1gr after fl sizing, trimming, uniforming the flash hole.
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.204 ruger , casing , moa , rl-15

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