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Rifles, Reloading, Optics, Equipment
Reloading
Case weight vs internal volume
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<blockquote data-quote="Mikecr" data-source="post: 961531" data-attributes="member: 1521"><p>You're right the cases do have to be fully prepped and fully fireformed to measure H20 capacity.</p><p>No need to clean cases beyond normal vibratory(the carbon film is fine).</p><p></p><p>It's initial volume/load density that sets up the peak in pressure curve, much like neck tension does. </p><p>By the time brass displacement variance in your chamber would come into play(expansion ratio), it is completely irrelevant. Much of what really matters to tune has well past by then.</p><p></p><p>But this does bring to point the fact that brass weight itself is meaningless to initial volume. You can crush those cases with a hammer to near zero volume -and they still weigh the same..</p><p>You can size down half of same weight cases enough to show differently across a chrono than the other half, because with the same charge, load density is different between the two volumes.</p><p></p><p>There is a work-around for this other than managing volume: Extreme pressure loads.</p><p>But this is only viable with little underbore cartridges like a 6PPC/30BR (not with most hunting capacity cartridges). Here, the pressure peak is in a return diminished region(in a sense) so that variance in it means 'relatively' less to tune. Load a 6PPC to normal pressures, hunting cartridge pressures, and it don't shoot like a competitive 6PPC anymore. It shoots more like a 6br or 223.</p><p>A 6.5x47L & 123gr bullet is pretty much the upper extent for this approach, and only with a magnum action to get enough barrel steel around the chamber.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 961531, member: 1521"] You're right the cases do have to be fully prepped and fully fireformed to measure H20 capacity. No need to clean cases beyond normal vibratory(the carbon film is fine). It's initial volume/load density that sets up the peak in pressure curve, much like neck tension does. By the time brass displacement variance in your chamber would come into play(expansion ratio), it is completely irrelevant. Much of what really matters to tune has well past by then. But this does bring to point the fact that brass weight itself is meaningless to initial volume. You can crush those cases with a hammer to near zero volume -and they still weigh the same.. You can size down half of same weight cases enough to show differently across a chrono than the other half, because with the same charge, load density is different between the two volumes. There is a work-around for this other than managing volume: Extreme pressure loads. But this is only viable with little underbore cartridges like a 6PPC/30BR (not with most hunting capacity cartridges). Here, the pressure peak is in a return diminished region(in a sense) so that variance in it means 'relatively' less to tune. Load a 6PPC to normal pressures, hunting cartridge pressures, and it don't shoot like a competitive 6PPC anymore. It shoots more like a 6br or 223. A 6.5x47L & 123gr bullet is pretty much the upper extent for this approach, and only with a magnum action to get enough barrel steel around the chamber. [/QUOTE]
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Case weight vs internal volume
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