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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Questions about internal ballistics: cartridge pressure and caliber vs velocity
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<blockquote data-quote="atl5029" data-source="post: 1013865" data-attributes="member: 84273"><p>I have some questions about cartridge pressure vs caliber and how it affects bullet velocity... </p><p> </p><p>I am familiar with the concept of bolt thrust, where for 2 cartridges operating at the same pressure, the one with the larger diameter case head will put a greater rearward force on the bolt due to Force=Pressure x area. Therefore it seems logical that the same thing should happen on the other end of the cartridge: a bigger caliber bullet would have more area for the pressure to act upon, resulting in a larger force to push it out of the barrel, and hence greater velocity. This is not often what we see however. Usually bigger rounds based on the same case as a smaller round are slower. Now I realize several things account for this. First, bigger caliber bullets are usually heavier, and therefore require more force to have an equal acceleration down the barrel. And second, a larger caliber bullet will have more bearing surface, which translates into a larger frictional force against forward motion. </p><p> </p><p>But what about cartridges of comparable caliber and bullet weight? I have been reading a lot lately about cartridges based on the 300 RUM case, and it seems like people are getting some really high velocities with the larger calibers above .338. I have read accounts on this forum of people reaching just over 3000 FPS with a 416-300 RUM with a 340 grain Cutting Edge bullet. And I know With a 338 Edge and 300 grain bullets, people often get around 2900 FPS, so it seems like despite the heavier bullet of 40 grains and larger bearing surface, the larger diameter bullet is able to be pushed faster. Does anyone have any solid insight into the mechanics of how these phenomena work? I would love a good physics/mechanics discussion.</p></blockquote><p></p>
[QUOTE="atl5029, post: 1013865, member: 84273"] I have some questions about cartridge pressure vs caliber and how it affects bullet velocity... I am familiar with the concept of bolt thrust, where for 2 cartridges operating at the same pressure, the one with the larger diameter case head will put a greater rearward force on the bolt due to Force=Pressure x area. Therefore it seems logical that the same thing should happen on the other end of the cartridge: a bigger caliber bullet would have more area for the pressure to act upon, resulting in a larger force to push it out of the barrel, and hence greater velocity. This is not often what we see however. Usually bigger rounds based on the same case as a smaller round are slower. Now I realize several things account for this. First, bigger caliber bullets are usually heavier, and therefore require more force to have an equal acceleration down the barrel. And second, a larger caliber bullet will have more bearing surface, which translates into a larger frictional force against forward motion. But what about cartridges of comparable caliber and bullet weight? I have been reading a lot lately about cartridges based on the 300 RUM case, and it seems like people are getting some really high velocities with the larger calibers above .338. I have read accounts on this forum of people reaching just over 3000 FPS with a 416-300 RUM with a 340 grain Cutting Edge bullet. And I know With a 338 Edge and 300 grain bullets, people often get around 2900 FPS, so it seems like despite the heavier bullet of 40 grains and larger bearing surface, the larger diameter bullet is able to be pushed faster. Does anyone have any solid insight into the mechanics of how these phenomena work? I would love a good physics/mechanics discussion. [/QUOTE]
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Questions about internal ballistics: cartridge pressure and caliber vs velocity
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