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Rifles, Reloading, Optics, Equipment
Reloading
Temp sensitivity
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<blockquote data-quote="MNbogboy" data-source="post: 797943" data-attributes="member: 18849"><p>I find this post very interesting..</p><p>The OPs idea his first post of averaging chrono results</p><p> is pretty much what a lot of us do when developing loads at different temps..</p><p>Bart B was spot on when mentioned about chamber time and the thermal co-efficients of brass & powder...</p><p>Everyone will see big differences from time to time especially with warm temps...</p><p>Big mistake everybody makes sooner or later is to leave your live ammo out in the sun...</p><p>That brass "sucks" up heat from the sun fast, faster than the powder inside warms up by far..</p><p>Just a minute or two in the sun and the chrono usually shows it as a fast one and sometimes a beginner will blame the powder...</p><p>One theory is; with the "hot" brass, the heat transfer during the combustion is slowed and more energy is left to push the bullet..This is makes some sense and agrees with Newton..</p><p>Can we calculate and predict exactly how much?...</p><p>Probably not unless we had a lot more information including all the barrel dynamics including the dimensional/tempural changes a barrel makes as energy is applied from its external & internal enviroments.. </p><p>But we can use our range data or even set up tests to get a better handle on it...</p><p>I often mark in my notes of extra chamber time with an individual shot..</p><p>These "usually" show extra velocity and sometimes I eliminate these from SD calcs...</p><p>This is "usually" depending on where the barrel is in its warm up cycle.</p><p>Personally I shoot all year long from below zero temps to 90 above and have never worried about powder temp sensitivity.</p><p>There are many more things you can try to control that will have a bigger effect on your results..</p><p>My opinion/advise is to collect your data in detail as you work up loads.</p><p>If you can not reach your goal over a wide range of temps with one powder or charge you may have to change powder or compromise velocity, but you can get there. </p><p>With all the data you collect you will be able to adjust for and shoot well with any conditions. </p><p>Randy</p></blockquote><p></p>
[QUOTE="MNbogboy, post: 797943, member: 18849"] I find this post very interesting.. The OPs idea his first post of averaging chrono results is pretty much what a lot of us do when developing loads at different temps.. Bart B was spot on when mentioned about chamber time and the thermal co-efficients of brass & powder... Everyone will see big differences from time to time especially with warm temps... Big mistake everybody makes sooner or later is to leave your live ammo out in the sun... That brass "sucks" up heat from the sun fast, faster than the powder inside warms up by far.. Just a minute or two in the sun and the chrono usually shows it as a fast one and sometimes a beginner will blame the powder... One theory is; with the "hot" brass, the heat transfer during the combustion is slowed and more energy is left to push the bullet..This is makes some sense and agrees with Newton.. Can we calculate and predict exactly how much?... Probably not unless we had a lot more information including all the barrel dynamics including the dimensional/tempural changes a barrel makes as energy is applied from its external & internal enviroments.. But we can use our range data or even set up tests to get a better handle on it... I often mark in my notes of extra chamber time with an individual shot.. These "usually" show extra velocity and sometimes I eliminate these from SD calcs... This is "usually" depending on where the barrel is in its warm up cycle. Personally I shoot all year long from below zero temps to 90 above and have never worried about powder temp sensitivity. There are many more things you can try to control that will have a bigger effect on your results.. My opinion/advise is to collect your data in detail as you work up loads. If you can not reach your goal over a wide range of temps with one powder or charge you may have to change powder or compromise velocity, but you can get there. With all the data you collect you will be able to adjust for and shoot well with any conditions. Randy [/QUOTE]
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