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Rifles, Reloading, Optics, Equipment
Reloading
Temperature and humidity factor - how do they affect my loads?
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<blockquote data-quote="Bart B" data-source="post: 115799" data-attributes="member: 5302"><p>Temperature and humidity do effect ballistic coefficient. BC goes higher as they get higher. Sierra's reloading manual has excellent technical explanations. A good ballistics software program could show the effects on a given cartridge's trajectory both will have when they change.</p><p></p><p>Shooting cold ammo from a cooler will result in a lower muzzle velocity providing you shoot each round as soon as it's chambered. Leave that cold round in a hot barrel more than 30 seconds and the powder will heat up then produce a higher muzzle velocity to require about a 1/4th MOA elevation change up for each minute it's in the barrel.</p><p></p><p>Hot ammo or cold, its bullets will still go through the ambient temperature, humidity and atmospheric pressure conditions the round's fired in. To see changes in trajectory for different atmospheres, you just about gotta shoot in them then record your sight settings for each one when that particular load's used.</p><p></p><p>A good barrel properly fitted won't change point of impact as it heats up and rounds aren't left in the chamber more than 30 seconds before they're fired. I've never seen any accuracy change from 20 to 105 degrees F, 5 to 90 percent humidity and 200 to 8300 feet altitude with the same rifle and ammo so I don't think bedding changes any significant amount. But sight elevation zero settings will change.</p></blockquote><p></p>
[QUOTE="Bart B, post: 115799, member: 5302"] Temperature and humidity do effect ballistic coefficient. BC goes higher as they get higher. Sierra's reloading manual has excellent technical explanations. A good ballistics software program could show the effects on a given cartridge's trajectory both will have when they change. Shooting cold ammo from a cooler will result in a lower muzzle velocity providing you shoot each round as soon as it's chambered. Leave that cold round in a hot barrel more than 30 seconds and the powder will heat up then produce a higher muzzle velocity to require about a 1/4th MOA elevation change up for each minute it's in the barrel. Hot ammo or cold, its bullets will still go through the ambient temperature, humidity and atmospheric pressure conditions the round's fired in. To see changes in trajectory for different atmospheres, you just about gotta shoot in them then record your sight settings for each one when that particular load's used. A good barrel properly fitted won't change point of impact as it heats up and rounds aren't left in the chamber more than 30 seconds before they're fired. I've never seen any accuracy change from 20 to 105 degrees F, 5 to 90 percent humidity and 200 to 8300 feet altitude with the same rifle and ammo so I don't think bedding changes any significant amount. But sight elevation zero settings will change. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Temperature and humidity factor - how do they affect my loads?
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