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Rifles, Reloading, Optics, Equipment
Reloading
Help with velocity variance
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<blockquote data-quote="boomtube" data-source="post: 454375" data-attributes="member: 9215"><p>"From my background in physics it ..."</p><p> </p><p>Okay, with your background in physics, convert the temps you tested to absolute temps and calculate the percentage of potential pressure change. And then consider that the temp<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite7" alt=":p" title="Stick Out Tongue :p" loading="lazy" data-shortname=":p" />ressure variations you calculate are static, they will be valid ONLY for the ignition phase, just a few nanoseconds. The rest of the massive delta temp<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite7" alt=":p" title="Stick Out Tongue :p" loading="lazy" data-shortname=":p" />ressure rise will be the normal powder burn temps for your load. The end temp is <em>really</em> hot by anyone's standards so the start temp is a fairly minor factor! </p><p> </p><p>So, yeah, sure it "matters." But not a lot.</p><p> </p><p>Again, physics for the chronograph/muzzle distance thing; Air in the bore is ejected in a straight line ahead of the bullet. That puts a very high density blast of air, a shock wave, out of the bore before the bullet exits. The chronograph's photo cells look for a change in light intensity to trigger the start count. IF the frontal density change in that air blast causes the cells see a light change we will get false triggering; not good. The photo screens have to be far enough from the muzzle to let that air blast dissipate and let the bullet do the job; 12-15 ft is usually okay.</p></blockquote><p></p>
[QUOTE="boomtube, post: 454375, member: 9215"] "From my background in physics it ..." Okay, with your background in physics, convert the temps you tested to absolute temps and calculate the percentage of potential pressure change. And then consider that the temp:pressure variations you calculate are static, they will be valid ONLY for the ignition phase, just a few nanoseconds. The rest of the massive delta temp:pressure rise will be the normal powder burn temps for your load. The end temp is [I]really[/I] hot by anyone's standards so the start temp is a fairly minor factor! So, yeah, sure it "matters." But not a lot. Again, physics for the chronograph/muzzle distance thing; Air in the bore is ejected in a straight line ahead of the bullet. That puts a very high density blast of air, a shock wave, out of the bore before the bullet exits. The chronograph's photo cells look for a change in light intensity to trigger the start count. IF the frontal density change in that air blast causes the cells see a light change we will get false triggering; not good. The photo screens have to be far enough from the muzzle to let that air blast dissipate and let the bullet do the job; 12-15 ft is usually okay. [/QUOTE]
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Help with velocity variance
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