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<blockquote data-quote="Dave King" data-source="post: 1940" data-attributes="member: 3"><p>Okay Len... I'll try too.</p><p></p><p></p><p> Express</p><p></p><p> Gravity acts by pulling objects toward the center of the earth (for our purposes). If we fire a projectile horizontal to the earth's surface and that projectile trys to fall to the center of the earth at a rate of oh... let's say 2.5 inches in a tenth of a second. A shooters we need to compensate by angling the barrel of the rifle upward (zeroing the rifle is how we do this) by this 2.5 inches for a shot taking one-tenth of a second, about 100 yards. Now let's see what happens when we use a worst case example... leave the rifle zeroed so there is a 2.5 inch up angle on the sights (horizontal 100 yard zero) and shoot straight down for a 100 yard shot. When we shoot straight down the effect of gravity is in the same direction as the projetile is traveling so the extra 2.5 inches of "drop" caused by gravity is changed from movement away from the line-of-flight to with the line of flight... and in effect there is no angular departure for the projectile BUT the rifle has 2.5 inches of "zero" (angular correction) built in and we'll shoot "high" by those 2.5 inches for a 100 yard shot.</p><p></p><p>To correct this 2.5 inch "high" miss we recalculate the line-of-sight distance by using the cosine of the angle to the target... cosine of 90 degrees is 0 (zero) and the one-tenth of a second flight time is about a 100 yard shot distance. 100 x 0 = 0 so we figure the distance at zero and set the scope for that distance. For a 60 degree shot the cosine is .5 so our distances will be 1/2 of the line-of-sight (laser) distance and for a 300 yard shot we'll set the scope as if it were a 150 yard shot. The concept once understood is simple...the solution(s) are several and it depends of how nit-picky you are as to how you fix the problem... I like to make it as difficult as possible and play with all kinds of numbers (and Excedrin) in an attempt to make an exact answer... the Angle Cosine Indicator and tools of it's like are functionally adequate and correct. </p><p></p><p>P. S. Don't try the above 90 degree example by shooting straight up in the air... you'll put your eye out <img src="http://images/icons/wink.gif" alt="" class="fr-fic fr-dii fr-draggable " style="" />.</p></blockquote><p></p>
[QUOTE="Dave King, post: 1940, member: 3"] Okay Len... I'll try too. Express Gravity acts by pulling objects toward the center of the earth (for our purposes). If we fire a projectile horizontal to the earth's surface and that projectile trys to fall to the center of the earth at a rate of oh... let's say 2.5 inches in a tenth of a second. A shooters we need to compensate by angling the barrel of the rifle upward (zeroing the rifle is how we do this) by this 2.5 inches for a shot taking one-tenth of a second, about 100 yards. Now let's see what happens when we use a worst case example... leave the rifle zeroed so there is a 2.5 inch up angle on the sights (horizontal 100 yard zero) and shoot straight down for a 100 yard shot. When we shoot straight down the effect of gravity is in the same direction as the projetile is traveling so the extra 2.5 inches of "drop" caused by gravity is changed from movement away from the line-of-flight to with the line of flight... and in effect there is no angular departure for the projectile BUT the rifle has 2.5 inches of "zero" (angular correction) built in and we'll shoot "high" by those 2.5 inches for a 100 yard shot. To correct this 2.5 inch "high" miss we recalculate the line-of-sight distance by using the cosine of the angle to the target... cosine of 90 degrees is 0 (zero) and the one-tenth of a second flight time is about a 100 yard shot distance. 100 x 0 = 0 so we figure the distance at zero and set the scope for that distance. For a 60 degree shot the cosine is .5 so our distances will be 1/2 of the line-of-sight (laser) distance and for a 300 yard shot we'll set the scope as if it were a 150 yard shot. The concept once understood is simple...the solution(s) are several and it depends of how nit-picky you are as to how you fix the problem... I like to make it as difficult as possible and play with all kinds of numbers (and Excedrin) in an attempt to make an exact answer... the Angle Cosine Indicator and tools of it's like are functionally adequate and correct. P. S. Don't try the above 90 degree example by shooting straight up in the air... you'll put your eye out [img]images/icons/wink.gif[/img]. [/QUOTE]
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