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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: 961602" data-attributes="member: 1521"><p>Look at it as INITIAL CONFINEMENT. Very similar to neck tension affecting initial confinement and changing the pressure curve enough to affect tune.</p><p>Initial confinement can change load density and speed or slow powder burn rate.</p><p></p><p>You put a little powder in a case without tamping & fire it, you get WHUMP. </p><p>Put a bit of COW, or even a single piece of toilet paper on top of the powder & fire it, you get BOOM.</p><p></p><p>A load density test:</p><p>Load two equal capacity rounds to about ~90% load density.</p><p>At the range, point the barrel straight up, load one of the rounds, carefully lower the gun to a rest, and fire across a chrono.</p><p>Now point the barrel down, load the other round, carefully raise it to rest and fire across a chrono.</p><p>You'll likely get abnormal ES between them, even though the cases match in capacity & regardless of case weight or it's chamber displacement.</p><p></p><p>Now imagine two equal weight cases, one FL sized every time, and the other never body sized at all. These cases will measure different in volume, and with the same load they will produce different muzzle velocities. It's not a lot of MV difference, you might not even see it with a cheap chrono, but it's there. And the peak pressure curve is also affected and your grouping results could change if these cases are mixed together in a string.</p><p>It's similar to mixing different brands or lots of brass.</p><p>And yes, different brands of brass present different capacities(volume).</p></blockquote><p></p>
[QUOTE="Mikecr, post: 961602, member: 1521"] Look at it as INITIAL CONFINEMENT. Very similar to neck tension affecting initial confinement and changing the pressure curve enough to affect tune. Initial confinement can change load density and speed or slow powder burn rate. You put a little powder in a case without tamping & fire it, you get WHUMP. Put a bit of COW, or even a single piece of toilet paper on top of the powder & fire it, you get BOOM. A load density test: Load two equal capacity rounds to about ~90% load density. At the range, point the barrel straight up, load one of the rounds, carefully lower the gun to a rest, and fire across a chrono. Now point the barrel down, load the other round, carefully raise it to rest and fire across a chrono. You'll likely get abnormal ES between them, even though the cases match in capacity & regardless of case weight or it's chamber displacement. Now imagine two equal weight cases, one FL sized every time, and the other never body sized at all. These cases will measure different in volume, and with the same load they will produce different muzzle velocities. It's not a lot of MV difference, you might not even see it with a cheap chrono, but it's there. And the peak pressure curve is also affected and your grouping results could change if these cases are mixed together in a string. It's similar to mixing different brands or lots of brass. And yes, different brands of brass present different capacities(volume). [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Case weight vs internal volume
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