You bring up five related but distinctly different basic properties of powders burning in cartridges. Look at the fundamentals (none of this is dreamt-up theory, BTW. It's all discerned and repeatedly confirmed fact):
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<br>First -- in a case with a given net capacity, larger charges of a given powder produce higher pressures.
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<br>Second -- In a larger case, a larger charge is necessary to produce the same level of pressure that the smaller charge produces in the smaller case.
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<br>Third -- at a given level of pressure, a smaller bore erodes faster than a larger bore (a .224 barrel erodes faster -- with fewer rounds fired -- than a .243 barrel if both the .224 and the .243 produce the same peak pressure). Like everything else involved here, this occurs in a mathematically calculable ratio.
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<br>Fourth -- powder produces velocity -- more powder produces more velocity. The amount of propelling gas produces velocity, whatever the peak pressure may be.
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<br>Five -- given the above, if larger Case B requires (for example) 10% more powder to produce the pressure that the smaller Case A produces, loading Case B with only 5% more powder can produce higher velocity at a lower pressure than Case A would require.
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<br>Given the huge variety of cartridges available for each bullet caliber, it isn't necessary to load a cartridge to SAAMI maximum pressures and above to get even the highest velocities safely available in the smaller cartridge. This is the "secret" of my .220 Howell, which uses a little more powder than the .220 Swift (for more velocity) in a 25% to 30% larger combustion cavity (for lower pressure, therefore slower throat erosion).
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<br>I wish this set of interlocking interior-ballistics principles weren't so widely unknown among serious handloaders. They're certainly easy enough to understand -- easier by far to exploit.
