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Rifles, Reloading, Optics, Equipment
Reloading
Load Density, Bullet Jump, Case Air Space
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<blockquote data-quote="MagnumManiac" data-source="post: 2261504" data-attributes="member: 10755"><p>Packing scheme plays a huge role in consistent charges.</p><p>If you look at a partially filled case like this, you will see why the air gap is not wanted, sometimes it is unavoidable, but if you think of a cartridge like a popcorn kettle when they blow air in it to mix the popcorn with the butter and salt, the more space there is, the more aerated it becomes.</p><p>The primer ignition pressure does the same thing when there is an air gap, the powder is forced away from the flash hole.</p><p>Poor ignition can result because the primer flash doesn't enter the powder column, it gets blown through the loose kernels and doesn't ignite as many kernels as the heat is transferred into air and not powder.</p><p>This is why in overbore (for want of a better description) cases like the 264WM work best, and produce better curves under MAP when extremely slow bulky powders are used. Even with Retumbo, there is still some space above the powder column.</p><p>In these instances, a FCD (factory crimp die) approach can help with ignition by delaying bullet movement momentarily allowing the burning powder to ignite properly before the bullet is released gaining a proper curve under MAP.</p><p>A flash over is when there is so much air space that ignition fizzles and the bullet moves but stops, but then ignites again and causes a pressure spike. Seen it myself in a Marlin 1895 45-70 where H4895 left unburnt powder everywhere but caused the lever to lock up. Only part of the powder ignited, even with a crimp.</p><p>Anyway, there is more to this, types of powder also contribute to this.</p><p></p><p>Cheers.</p></blockquote><p></p>
[QUOTE="MagnumManiac, post: 2261504, member: 10755"] Packing scheme plays a huge role in consistent charges. If you look at a partially filled case like this, you will see why the air gap is not wanted, sometimes it is unavoidable, but if you think of a cartridge like a popcorn kettle when they blow air in it to mix the popcorn with the butter and salt, the more space there is, the more aerated it becomes. The primer ignition pressure does the same thing when there is an air gap, the powder is forced away from the flash hole. Poor ignition can result because the primer flash doesn’t enter the powder column, it gets blown through the loose kernels and doesn’t ignite as many kernels as the heat is transferred into air and not powder. This is why in overbore (for want of a better description) cases like the 264WM work best, and produce better curves under MAP when extremely slow bulky powders are used. Even with Retumbo, there is still some space above the powder column. In these instances, a FCD (factory crimp die) approach can help with ignition by delaying bullet movement momentarily allowing the burning powder to ignite properly before the bullet is released gaining a proper curve under MAP. A flash over is when there is so much air space that ignition fizzles and the bullet moves but stops, but then ignites again and causes a pressure spike. Seen it myself in a Marlin 1895 45-70 where H4895 left unburnt powder everywhere but caused the lever to lock up. Only part of the powder ignited, even with a crimp. Anyway, there is more to this, types of powder also contribute to this. Cheers. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Load Density, Bullet Jump, Case Air Space
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