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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Effects of Rifle Canting on LR Accuracy
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<blockquote data-quote="Dave King" data-source="post: 28654" data-attributes="member: 3"><p>Brent</p><p></p><p> Okay... you've got me doing cartwheels in Excel...</p><p></p><p> I was doing this/these calulation once before and now I'm getting the hang of the problem.</p><p></p><p> I believe the magnitude of the problem with cant is that it's contrary to inclined fire (cosine) logic solution. The cosine as used in inclined fire indicates that when deviating from a 90 degree from the horizontal the initial "gradiant/step" values are small and the final steps are large. The degree of deviation for a 45 degree inclined fire problem is 1 - .707 or .293. BUT the deviation for a cant problem (as I see it) is greatest at the onset so a 45 degree cant produces a deviation error of .707 not the .293 I had expected.</p><p></p><p> A cant angle of 30 degrees produces a windage error of 50%, as a result as rifle zeroed at 100 yards with the scope set at 100 yards will have a deviation for elevation and windage. For my 308 Win with a 1.75" scope height and 2.7 inches of TOF drop I'll have a 2.225" windage error and a -.6" elevation error.</p><p></p><p> Now if I think of what happens when (we) add elevation to a scope. The termination of the line-of-sight departure angle should now become the basis for the error determination. (View this as a cone of departure, point at the muzzle with the depth of the cone equal to the yardage value and the base of the cone double the elevation requirement.) So your ~276 inches of drop and 12 degrees of cant produce a (276 + 1.76) * .2079 (the Cosine of 90-12 or 78 degrees) = 57.75 inch windage error at 1000 yards. The elevation error is the reciprocal of the windage error (I believe) so (276 + 1.76) * .021852 ( 1 minus the cosine of 12 or .978148) for an elevation deviation of about 6.06 inches.</p><p></p><p>Does any of this make sense? Hope I'm about on the correct train of thought.</p><p></p><p>BTW... Thanks for getting me back onto this puzzle.</p><p></p><p>[ 09-25-2003: Message edited by: Dave King ]</p></blockquote><p></p>
[QUOTE="Dave King, post: 28654, member: 3"] Brent Okay... you've got me doing cartwheels in Excel... I was doing this/these calulation once before and now I'm getting the hang of the problem. I believe the magnitude of the problem with cant is that it's contrary to inclined fire (cosine) logic solution. The cosine as used in inclined fire indicates that when deviating from a 90 degree from the horizontal the initial "gradiant/step" values are small and the final steps are large. The degree of deviation for a 45 degree inclined fire problem is 1 - .707 or .293. BUT the deviation for a cant problem (as I see it) is greatest at the onset so a 45 degree cant produces a deviation error of .707 not the .293 I had expected. A cant angle of 30 degrees produces a windage error of 50%, as a result as rifle zeroed at 100 yards with the scope set at 100 yards will have a deviation for elevation and windage. For my 308 Win with a 1.75" scope height and 2.7 inches of TOF drop I'll have a 2.225" windage error and a -.6" elevation error. Now if I think of what happens when (we) add elevation to a scope. The termination of the line-of-sight departure angle should now become the basis for the error determination. (View this as a cone of departure, point at the muzzle with the depth of the cone equal to the yardage value and the base of the cone double the elevation requirement.) So your ~276 inches of drop and 12 degrees of cant produce a (276 + 1.76) * .2079 (the Cosine of 90-12 or 78 degrees) = 57.75 inch windage error at 1000 yards. The elevation error is the reciprocal of the windage error (I believe) so (276 + 1.76) * .021852 ( 1 minus the cosine of 12 or .978148) for an elevation deviation of about 6.06 inches. Does any of this make sense? Hope I'm about on the correct train of thought. BTW... Thanks for getting me back onto this puzzle. [ 09-25-2003: Message edited by: Dave King ] [/QUOTE]
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Effects of Rifle Canting on LR Accuracy
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