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Old 12-12-2018, 02:35 PM   #1
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Do bottleneck cartridges increase pressure?

Wanted to ask a question that puzzles me. Do bottleneck cartridges increase pressure? I can load 22gr. of H110 under a 110gr. bullet and achieve about 35,000 PSI. However, if I load 22gr. of H322 in a .223 case under a 69gr. bullet I'm loading about 55,000 PSI. Why does a smaller case (.357) with a much faster powder and a heavier bullet result in less pressure? I was told that a bottleneck cartridge does not increase pressure. What goes?
Thanks in advance and good shooting' to ya, Dgang
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Old 12-13-2018, 11:51 AM   #2
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Two things and both are related to case volume and bullet weight: first, burn rate. The faster burning powder will increase pressure faster. Second, a safety component. The heavier bullet has greater inertia (Newtons laws of motion). Higher pressure offers a potential risk of over pressure.
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Old 03-31-2019, 11:55 PM   #3
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Internal ballistics is a very complicated subject. A bottleneck case also can be looked at as a combination combustion chamber and built-in rocket nozzle, and as the nozzle gets smaller, pressures can build up in the combustion chamber.
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Old 04-01-2019, 12:25 PM   #4
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To save having to delve into a course on physics, I suggest looking at one of the many books available - reloading manuals included - that address ballistics. A familiarity with the venturi principle is also helpful when discussing bottleneck cartridges- or as noyli hinted - rocket engine nozzles.
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Old 04-05-2019, 04:27 PM   #5
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Agree gotta look it up and find out some real info vs what some may claim they know about it
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Old 04-05-2019, 05:31 PM   #6
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From a physics perspective in the end - given a closed, sealed container - the significant factors are how quickly and how much (potentially) pressure is created, and how quickly the pressure (think number and size of apertures created) is able to escape.
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