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Old February 12, 2013, 08:25 AM   #28
Join Date: March 4, 2005
Location: Ohio
Posts: 13,648
Powder bulk density can vary several percentage points from lot to lot, so measuring the N135 won't help. In particular, stick powder can also pack down quite a bit, depending how much vibration it is subjected to. Below is the same charge that went through different length drop tubes, which causes the grains to bounce around to randomly find tighter packing configurations:

Looks like your cases are lighter than Lapua. Below is the distribution for 30 cases from the last Lapua cases I bought. You can plainly see the output of two tool sets segregating into two groups. The sample size would need to double for them to more closely resemble symmetrical bell curves. They average 172.56 Yours are 165.91. The difference divided by 14 is 0.475 gr., so you can expect your cases to hold about 0.5 grains more powder to reach the same pressure as new Lapua cases would give you. So that's an adjustment you could make to Lapua load data. When you get time to find water capacity of fireformed cases, we'll have an adjustment for your chamber.

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