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Old February 11, 2013, 05:36 PM   #26
Pond, James Pond
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Also, if you have time, do a case water overflow capacity measurement.
How about if I filled a primed case to the brim full of N135, and did it for 5 or so cases, then measured what was held in a case. Particularly as a primed case is also clean on the inside.

Between the average weight of those full case loads and the density of the powder, would that not also give you similar values for internal volume, or is water that much more accurate?
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Old February 11, 2013, 06:34 PM   #27
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Water is the more accurate, and is the basis for all case comparisons
that you will find in standard references (and all across the Web)
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Old February 12, 2013, 08:25 AM   #28
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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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Old February 12, 2013, 11:21 AM   #29
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Mehavey states water is the more accurate, and is the basis for all case comparisons that you will find in standard references (and all across the Web). Go figure out what the difference in water capacity for a give case with different amounts of out of round diameters and you'll disagree with this. Look closely on the web and you'll also find top ranked competitors sorting cases by weight. But case water capacity is the one most e-talked about.

The group of 4 folks I know of shooting the .308 Win. (and other cartridges) the best for accuracy (machine rest tested) and collectively having the most Nat'l Championships, matches won and records set, all use cases sorted by weight.

=====================

Unclenick, Lapua's been known to package some cases and bullets from two or more sets of coin, cup, draw and shape dies in the same retail box so that two-humped case weight curve is not surprising to me. A friend checked several hundred Lapua match bullets on an optical comparitor and found 4 distinctly different shapes of rebated base and ogive contours on their D46 185-gr. FMJRB match bullets.
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Old February 12, 2013, 03:34 PM   #30
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Yep. I've been doing histograms like that for awhile just to spot how many tool sets were involved. The width gives you sorting information. Here's one for some Winchester brass that I actually did using some new bulk purchase Winchester cases, but later drew from that data.



Here's a photo of a sort of some LC .30-06 brass by neck wall runout. The left side is zero (actually <0.0005" TIR) then in 0.001" steps to the right:



Regarding water capacity, the main purpose is to allow for the individual chamber's size, which is mainly useful for getting QuickLOAD optimized for a particular rifle. Once you've found your load workup range, though, as you say, just going by case weight difference is really all you need or, unless you're nuts, want to take the time to do.

I find water capacity prediction from weight is usually within 20%, with the error due mainly to differences in head diameters and differences in the angle off the extractor groove going forward. So when I suggest Mr. Pond's Norma cases will need half a grain (actually 0.48 grains) more powder to match the pressure of loads developed in Lapua brass, that may actually be off by about ±0.08 grains. Close enough.
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Old May 11, 2013, 02:41 PM   #31
Pond, James Pond
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Water capacity

I finally got some fired cases and measured the water capacity, as requested. The cases were uncleaned though, and had the spent primer.

The case alone was 170.2gr, and once full of water weighed 227.3gr.

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