The physics aren't simple when your observations aren't consistent with the anticipated results. I suspect there's something more complicated involved.
Likening the physics of a balloon to a shotshell, I assumed an all plastic hull without a separate base wad. Since you're using hulls with significant paper base wads, you've complicated a simple example.
Do the hulls you're using have the same height base wads? Obviously the base wads complicate the loading of the metal bases. If they aren't uniformly loaded, then different deflections may be anticipated. This explains what you're experiencing within the bounds of simple physics. (Remembering my undergraduate days, calculating deflections was a pain in the rear. Simple mechanics didn't seem so simple.)
Baltz526, have you tried unibody type plastic hulls? Perhaps you wouldn't experience the extractions problems if you eliminate the paper base wad hulls.
Over the years, I've gone through a king's ransom in shot shell components reloading for practice and competition. I've always looked for low pressure loads to reduce the wear and tear on the guns and my shoulder. From my perspective, a 11,600 psi 12-ga load is on the high side. I looked at some of my loading guides and didn't see any loads that high. Your guide may have loads that are 11,600 psi in their test barrels; but, that doesn't mean it's the same in your 870. Could some of your extraction problems be related to over-pressure? And, 870 Expresses have been the continuous subject of extraction difficulties.
Likening the physics of a balloon to a shotshell, I assumed an all plastic hull without a separate base wad. Since you're using hulls with significant paper base wads, you've complicated a simple example.
Do the hulls you're using have the same height base wads? Obviously the base wads complicate the loading of the metal bases. If they aren't uniformly loaded, then different deflections may be anticipated. This explains what you're experiencing within the bounds of simple physics. (Remembering my undergraduate days, calculating deflections was a pain in the rear. Simple mechanics didn't seem so simple.)
Baltz526, have you tried unibody type plastic hulls? Perhaps you wouldn't experience the extractions problems if you eliminate the paper base wad hulls.
Over the years, I've gone through a king's ransom in shot shell components reloading for practice and competition. I've always looked for low pressure loads to reduce the wear and tear on the guns and my shoulder. From my perspective, a 11,600 psi 12-ga load is on the high side. I looked at some of my loading guides and didn't see any loads that high. Your guide may have loads that are 11,600 psi in their test barrels; but, that doesn't mean it's the same in your 870. Could some of your extraction problems be related to over-pressure? And, 870 Expresses have been the continuous subject of extraction difficulties.
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