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Rifles, Reloading, Optics, Equipment
Reloading
New brass - different velocities than fire formed?
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<blockquote data-quote="Mikecr" data-source="post: 990923" data-attributes="member: 1521"><p>It don't matter where the dents are, and Phorwath's dented cases did fully expand to the chamber & springback. That there was some blowby is the nature of semi-auto chambers(loose). The gas would come & go where it logically would(least resistance). It could have gotten trapped, but it didn't in this case.</p><p></p><p>It's all about initial confinement.</p><p>If this is hard to picture capacity-wise, think of it as simple load density. The dent increased load density a little bit and a lot of times it don't take much.</p><p></p><p>If your cases were at ~90% fill(for real) you could run a test to see the same thing without dents.</p><p>Load a gun while it's pointed downward, ease it up to fire through a chronograph.</p><p>Then load the gun pointed up, and ease it down to fire across chrono.</p><p>The second shot will be higher in velocity, because relative load density has increased nearest ignition source. You've altered initial confinement.</p><p></p><p>Sure the cases expand to chamber dimensions. Hell it's takes little more than 100psi to do that. Brass might as well be tinfoil to a normal ~55Kpsi pressure peak.</p><p>And a charge laying very slightly tighter against a flash hole will blow forward **** quick.</p><p>But neither is fast enough to negate their affect by then. The powder ignition that causes these things was affected FIRST, and this can't just undo itself.</p><p>Most of what matters happens way before bullet movement.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 990923, member: 1521"] It don't matter where the dents are, and Phorwath's dented cases did fully expand to the chamber & springback. That there was some blowby is the nature of semi-auto chambers(loose). The gas would come & go where it logically would(least resistance). It could have gotten trapped, but it didn't in this case. It's all about initial confinement. If this is hard to picture capacity-wise, think of it as simple load density. The dent increased load density a little bit and a lot of times it don't take much. If your cases were at ~90% fill(for real) you could run a test to see the same thing without dents. Load a gun while it's pointed downward, ease it up to fire through a chronograph. Then load the gun pointed up, and ease it down to fire across chrono. The second shot will be higher in velocity, because relative load density has increased nearest ignition source. You've altered initial confinement. Sure the cases expand to chamber dimensions. Hell it's takes little more than 100psi to do that. Brass might as well be tinfoil to a normal ~55Kpsi pressure peak. And a charge laying very slightly tighter against a flash hole will blow forward **** quick. But neither is fast enough to negate their affect by then. The powder ignition that causes these things was affected FIRST, and this can't just undo itself. Most of what matters happens way before bullet movement. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
New brass - different velocities than fire formed?
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