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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
n570 temperature stability
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<blockquote data-quote="Veteran" data-source="post: 2316777" data-attributes="member: 118038"><p>Here's a link you may find helpful. In this link someone said that according to Vihtavuori's website, only N565 and N568 were claimed to be temperature insensitive. I don't know that for sure, its just what was said in another thread.</p><p></p><p>[URL unfurl="true"]https://www.longrangehunting.com/threads/temperature-sensitivity-experience-n560-and-rl-26.276712/[/URL]</p><p></p><p>Out of curiosity though I did some modeling in Quickload. I took my .338 LM data files for N560, N565, N568, and N570.</p><p></p><p>I varied the temperature by 30 degrees from 70 to 100 leaving all other inputs constant for each powder.</p><p></p><p>What I saw was a variance of about 1.23 to 1.66 FPS in velocity for each degree of temp. change for these powders. </p><p></p><p>N565 was the least sensitive only varying 1.23 FPS per degree. N568 and N570 were the most sensitive varying 1.63 to 1.66 FPS per degree. I note they are the lowest burn rates of these powders, and the way that Quickload handles the change in temperature is to modify the burn rate according to some correlation it has internally. So, the lowest burn rates were the most sensitive per degree of temp. change. Seems a little counterintuitive, but the N568 is a more fine grained cut, and the density may have some bearing, and the chemistry of these powders may also have some bearing. </p><p></p><p>If you are getting only 10 FPS change for 30-35 degrees change, you are doing better than expected IMHO.</p><p></p><p>It could be more like 30-50 FPS and at higher altitude, you can expect it to be that much or more just due to the difference in </p><p>air density out to range, (not at the muzzle, but over 300-1000 yards). Run some ballistics projections at your altitude with your sight in zero, and run them again at 10,000 feet with difference in station pressure, and altitude. See what the differences are in </p><p>velocity at distance. Its going to be more than you expect. Both due to temperature, and air density. That's why folks sighting in </p><p>on the Texas Gulf Coast at sea level end up shooting way over the backs of their elk up in the mountains. </p><p></p><p>Best to sight in and check everything on site before the hunt!</p><p></p><p>By the way, none of these powders are totally insensitive to temp. Not Retumbo, Not H1000, Not RL-26. They all can act bizzaro </p><p>under 95 degrees plus temp when you develop a hot load at 70 degree temp and take it into really hot weather, especially in a heated chamber or barrel.</p></blockquote><p></p>
[QUOTE="Veteran, post: 2316777, member: 118038"] Here's a link you may find helpful. In this link someone said that according to Vihtavuori's website, only N565 and N568 were claimed to be temperature insensitive. I don't know that for sure, its just what was said in another thread. [URL unfurl="true"]https://www.longrangehunting.com/threads/temperature-sensitivity-experience-n560-and-rl-26.276712/[/URL] Out of curiosity though I did some modeling in Quickload. I took my .338 LM data files for N560, N565, N568, and N570. I varied the temperature by 30 degrees from 70 to 100 leaving all other inputs constant for each powder. What I saw was a variance of about 1.23 to 1.66 FPS in velocity for each degree of temp. change for these powders. N565 was the least sensitive only varying 1.23 FPS per degree. N568 and N570 were the most sensitive varying 1.63 to 1.66 FPS per degree. I note they are the lowest burn rates of these powders, and the way that Quickload handles the change in temperature is to modify the burn rate according to some correlation it has internally. So, the lowest burn rates were the most sensitive per degree of temp. change. Seems a little counterintuitive, but the N568 is a more fine grained cut, and the density may have some bearing, and the chemistry of these powders may also have some bearing. If you are getting only 10 FPS change for 30-35 degrees change, you are doing better than expected IMHO. It could be more like 30-50 FPS and at higher altitude, you can expect it to be that much or more just due to the difference in air density out to range, (not at the muzzle, but over 300-1000 yards). Run some ballistics projections at your altitude with your sight in zero, and run them again at 10,000 feet with difference in station pressure, and altitude. See what the differences are in velocity at distance. Its going to be more than you expect. Both due to temperature, and air density. That's why folks sighting in on the Texas Gulf Coast at sea level end up shooting way over the backs of their elk up in the mountains. Best to sight in and check everything on site before the hunt! By the way, none of these powders are totally insensitive to temp. Not Retumbo, Not H1000, Not RL-26. They all can act bizzaro under 95 degrees plus temp when you develop a hot load at 70 degree temp and take it into really hot weather, especially in a heated chamber or barrel. [/QUOTE]
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