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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Dave King or JBM, Help! I found a ballistics problem!
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<blockquote data-quote="4ked Horn" data-source="post: 61631" data-attributes="member: 11"><p>[ QUOTE ]</p><p>You are shooting at 3000 ft elevation. You sight in your rifle so that it is exactly 3" high at 100 yards. Your program says that for your particular load, your zero is 300 yards.</p><p></p><p></p><p>Now, you go up to 8000 feet on a mule deer hunt. You bring your laptop with you and punch in your pet load and enter in the elevation of 8000 feet. The program now says that you are shooting 3.2" high at 100 yards because of the elevation change. You assume that because the thinner air makes your gun shoot .2" higher than before that you are now zeroed at a little over 300 yards.</p><p></p><p>[/ QUOTE ]</p><p></p><p>Air density is inversely proportional to ballistic coefficient. As the air gets thinner the effective BC rises. In other words if you shot a bullet with a 3000 fps muzzle velocity at sea level and then shoot this same bullet at 8000 feet elevation you should see similar results to shooting a higher BC bullet at 3000 fps MV at sea level.</p><p></p><p>What I'm trying to illustrate is that the thinner air should NOT Cause your bullet to have a higher trajectory at 100 yards. It should reach it's " 3" high" at a distance like 125 yards and it should be zeroed at something like 342 yards.(those numbers are just picked to illustrate my point I did not calculate them anywhere)</p><p></p><p>Gravity stays the same. The only difference should be a "stretching out" of the parabolic curve due to higher retained velocities at higher elevations. </p><p></p><p>For you to have a 300 yard zero at 8000 feet your bullets should print LOWER than 3" at 100 yards.</p></blockquote><p></p>
[QUOTE="4ked Horn, post: 61631, member: 11"] [ QUOTE ] You are shooting at 3000 ft elevation. You sight in your rifle so that it is exactly 3" high at 100 yards. Your program says that for your particular load, your zero is 300 yards. Now, you go up to 8000 feet on a mule deer hunt. You bring your laptop with you and punch in your pet load and enter in the elevation of 8000 feet. The program now says that you are shooting 3.2" high at 100 yards because of the elevation change. You assume that because the thinner air makes your gun shoot .2" higher than before that you are now zeroed at a little over 300 yards. [/ QUOTE ] Air density is inversely proportional to ballistic coefficient. As the air gets thinner the effective BC rises. In other words if you shot a bullet with a 3000 fps muzzle velocity at sea level and then shoot this same bullet at 8000 feet elevation you should see similar results to shooting a higher BC bullet at 3000 fps MV at sea level. What I'm trying to illustrate is that the thinner air should NOT Cause your bullet to have a higher trajectory at 100 yards. It should reach it's " 3" high" at a distance like 125 yards and it should be zeroed at something like 342 yards.(those numbers are just picked to illustrate my point I did not calculate them anywhere) Gravity stays the same. The only difference should be a "stretching out" of the parabolic curve due to higher retained velocities at higher elevations. For you to have a 300 yard zero at 8000 feet your bullets should print LOWER than 3" at 100 yards. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Dave King or JBM, Help! I found a ballistics problem!
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