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The Range
Rifle & Shotgun Discussion
7.5 inch AR Upper question
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<blockquote data-quote="omegis13" data-source="post: 743972" data-attributes="member: 4945"><p>For a subsonic round, 9mm will almost always carry more kinetic energy than a 5.56 projectile. Under Newtonian physics, the equation for kinetic energy is</p><p></p><p>E(k) = (mv^2)/2</p><p></p><p>where m = mass, v = velocity. At standard temp, pressure, and elevation, an object can move no faster than 1125 ft/s before it creates a sonic boom, but the exact speed we decide on here is really irrelevant, because in the experiment and the equation, it is a constant when considering both rounds. On any given day, fired under the same conditions, both a 9mm projectile and a .223 projectile will have to reach the same minimum speed in order to create a sonic boom, which for the sake of the experiment, is something we wish to avoid.</p><p></p><p>popular subsonic 9mm ammo seems to be at weights of 147gr and 158gr. Most of the weights I am seeing for subsonic 5.56 seem to float around 100gr.</p><p></p><p>Could a person theoretically manufacture a much lighter subsonic 9mm cartridge or a much heavier sub sonic 5.56 cartridge? Absolutely, but what's the point? When you have an upper boundary you must stay under such as the sound barrier, the only other option that exists for moving more energy with a projectile is increasing the mass of the projectile itself.</p></blockquote><p></p>
[QUOTE="omegis13, post: 743972, member: 4945"] For a subsonic round, 9mm will almost always carry more kinetic energy than a 5.56 projectile. Under Newtonian physics, the equation for kinetic energy is E(k) = (mv^2)/2 where m = mass, v = velocity. At standard temp, pressure, and elevation, an object can move no faster than 1125 ft/s before it creates a sonic boom, but the exact speed we decide on here is really irrelevant, because in the experiment and the equation, it is a constant when considering both rounds. On any given day, fired under the same conditions, both a 9mm projectile and a .223 projectile will have to reach the same minimum speed in order to create a sonic boom, which for the sake of the experiment, is something we wish to avoid. popular subsonic 9mm ammo seems to be at weights of 147gr and 158gr. Most of the weights I am seeing for subsonic 5.56 seem to float around 100gr. Could a person theoretically manufacture a much lighter subsonic 9mm cartridge or a much heavier sub sonic 5.56 cartridge? Absolutely, but what's the point? When you have an upper boundary you must stay under such as the sound barrier, the only other option that exists for moving more energy with a projectile is increasing the mass of the projectile itself. [/QUOTE]
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