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Altitude and zero
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<blockquote data-quote="entoptics" data-source="post: 2911810" data-attributes="member: 104268"><p>A bullet will drop less as elevation and/or temperature increases because air density decreases.</p><p></p><p>Unless you're zeroed at a heck of a long ways out, or using a very slow bullet with a terrible B.C. (45 ACP?), elevation will have a negligible effect on your zero point of impact. I ran the numbers from 2000-10000 ft, and it's less than or equal to ± 0.1 inches at 200 yards at either extreme. At 600 yards, it's about 0.5" - 1" per 1000 feet of change depending on B.C. and muzzle velocity.</p><p></p><p>For temperature, it's ~1/3" per 10° at 600 yards, and too small to register on JBM ballistics at 200 yards, because it's less than 0.1 which is all the decimals displayed.</p><p></p><p><strong>Inputs...</strong></p><p>0.275 G7 B.C. (~0.550 G1 B.C.) @ 2900 fps</p><p>Zeroed at 5000 ft, 29.92 sea level corrected pressure, 70° F, 40% RH.</p><p>Zero angle was fixed at the above zero conditions (e.g. you zeroed your rifle once, then shot that same zero in the variable conditions shown below without rezeroing to 200 yards again at the different conditions).</p><p></p><p>[ATTACH=full]496993[/ATTACH]</p><p></p><p>[ATTACH=full]496994[/ATTACH]</p><p></p><p></p><p>In summary, if your zero was off by 1.5" it's got nothing to do with temp or elevation, and is a result of some other issue.</p></blockquote><p></p>
[QUOTE="entoptics, post: 2911810, member: 104268"] A bullet will drop less as elevation and/or temperature increases because air density decreases. Unless you're zeroed at a heck of a long ways out, or using a very slow bullet with a terrible B.C. (45 ACP?), elevation will have a negligible effect on your zero point of impact. I ran the numbers from 2000-10000 ft, and it's less than or equal to ± 0.1 inches at 200 yards at either extreme. At 600 yards, it's about 0.5" - 1" per 1000 feet of change depending on B.C. and muzzle velocity. For temperature, it's ~1/3" per 10° at 600 yards, and too small to register on JBM ballistics at 200 yards, because it's less than 0.1 which is all the decimals displayed. [B]Inputs...[/B] 0.275 G7 B.C. (~0.550 G1 B.C.) @ 2900 fps Zeroed at 5000 ft, 29.92 sea level corrected pressure, 70° F, 40% RH. Zero angle was fixed at the above zero conditions (e.g. you zeroed your rifle once, then shot that same zero in the variable conditions shown below without rezeroing to 200 yards again at the different conditions). [ATTACH type="full"]496993[/ATTACH] [ATTACH type="full"]496994[/ATTACH] In summary, if your zero was off by 1.5" it's got nothing to do with temp or elevation, and is a result of some other issue. [/QUOTE]
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