"This large case-low pressure theory goes against the latest trend of the PPC design of the short fat case."
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<br>Not at all. The ratio of case diameter to case length is an entirely different design consideration that doesn't matter here.
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<br>"It also results in less than full cases that might result in secondary explosions as Ackley found with reduced loads and slow powders."
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<br>Nope. You've assumed "facts" not in evidence. The larger case uses a slower powder -- with benefits that I didn't present in the discussion of the other comparison. The pressure curve in the .220 Howell compares very interestingly with the Swift's curve. The Swift's curve rises quickly to a higher and sharper pressure peak, then fades rapidly as the bullet scoots toward the muzzle. The .220 Howell's curve rises more slowly to a significantly lower peak, then fades much more slowly with bullet travel. The PEAK pressure (read "erosion") is lower in the .220 Howell, while its AVERAGE pressure (read "acceleration") is higher, clear out to the muzzle.
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<br>"Overbore" is a word used often, understood seldom. My cartridges are not over bore capacity for the powders that I designed them around.
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<br>"Bore capacity" applies to a cartridge in relation to available powders. A case that's "over bore capacity" is a case that can not be loaded with a caseful of any available powder without developing dangerous pressures. It's a matter of how fast and how high the pressure curve rises while the travel of the bullet down the bore bleeds-off some of the pressure. In a case that's over bore capacity, the travel of the bullet down the bore can not relieve the building pressure fast enough to keep the peak pressure (from a caseful charge) down to a safe level.
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<br>If there's a powder available that you can fill the case with, without producing dangerous pressures, that case is not "over bore capacity."
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<br>When I started loading rifle ammo in the early 'Fifties, IMR-4350 and H-4831 were the slowest powders available. Both are too fast for the .220 Howell -- i e, the .220 Howell is over bore capacity for these powders (just as the .223 is over bore capacity for Bullseye). It is NOT, however, over bore capacity for IMR-7828, Ramshot Magnum, and several other powders in this burning-rate class. I could fill my .220 Howell with Hodgdon's ultra-slow 50BMG powder and not even come close to optimum pressures. I couldn't pack, jam, or stomp enough 50BMG into the .220 Howell to raise pressures to a good operating level -- so the .220 Howell is clearly NOT "over bore capacity" for all available powders.
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<br>As I've already posted somewhere, this isn't just nerd theory. It's all long-proven fact, clearly presented in classic interior-ballistics literature that unfortunately isn't available to the average shooter. So of course it's all "new" to you and seems to run counter to what you already know about what goes on inside the rifle. But the fact that it's new, and negates some of your understanding, does NOT mean that it's wrong. I'm not putting anybody down. Just the opposite -- I'm trying to share what I'm learning in intense study of interior ballistics.
