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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="Brent" data-source="post: 28653" data-attributes="member: 99"><p>Here's a chart at 1000 yards for the 308 win and a 175gr SMK with 12 degrees of rifle cant for comparison. More error is the result of much more MOA needed to zero it at 1000 than the other one.</p><p></p><p>CALIBER: 308 Win</p><p>MUZZLE VELOCITY: 2600 fps</p><p>BULLET WEIGHT: 175 gr.</p><p>BALLISTIC COEFFICIENT: 0.505</p><p>SIGHT HT.: 1.76 in. (1.8"/12°)</p><p>ZEROED AT: 997.9 Yds.</p><p>INCLINE ANGLE: 0 deg.</p><p>WIND: 0 mph</p><p>STANDING TARGET</p><p>ATMOSPHERE: Std. 300 ft. </p><p> 59° F./300 ft./29.53 in. HG/78% R.H.</p><p>'G1' STANDARD FLAT BASE</p><p></p><p>Range- Vel.- Energy- Drop- Path---- Defl.-- Time- Lead-</p><p>Yards- fps- Ft.Lbs.- Inches- MOA- Inches- Sec.- Inches-</p><p> </p><p>000 2600 2627 0.00 0.00 -0.37 0.000 0.0</p><p> </p><p>100 2428 2290 2.69 38.49 8.85 0.119 0.0</p><p> </p><p>200 2262 1988 11.29 36.51 18.08 0.247 0.0</p><p> </p><p>300 2102 1717 26.70 33.68 27.30 0.385 0.0</p><p> </p><p>400 1949 1477 49.99 30.39 36.53 0.533 0.0</p><p> </p><p>500 1804 1264 82.44 26.66 45.76 0.693 0.0</p><p> </p><p>600 1666 1079 125.60 22.47 54.98 0.866 0.0</p><p> </p><p>700 1537 918 181.31 17.77 64.21 1.054 0.0</p><p> </p><p>800 1419 782 251.74 12.48 73.44 1.257 0.0</p><p> </p><p>900 1312 669 339.47 6.54 82.66 1.477 0.0</p><p></p><p>1000 1219 577 447.41 -0.15 91.89 1.714 0.0</p><p></p><p>TRAJECTORY CROSSES LINE OF SIGHT AT 3.9 & 997.9 yds. </p><p>PATH IS 141.97 IN. OVER LINE OF SIGHT AT 566.4 yds.</p><p></p><p></p><p>After some figuring, I figure that a scope to rifle mounting angle error of 1 degree would equal .01111 MOA windage deflection for every 1 MOA elevation dialed for a farther range beyond the 100yd zero.</p><p></p><p>A 90 degree angle mounting cant error would obviously cause a 1 MOA windage correction if dialing in 1 MOA elevation. Half that cant angle, 45 degrees, would cause .5 MOA deflection and so on. So 1/90th of that is equal to .01111 MOA deflection per 1 MOA elevation dialed in if the scope is canted only 1 degree.</p><p></p><p>So if the "scope" alignment instead is off the same 12 degrees from the rifle when installed, the error at 1000 yards with the 38.61 MOA needed to rezero there, there would be .01111 * 12 * 38.61 * 10 = 51.47" or 4.91 MOA deflection error introduced. </p><p></p><p>That 4.91 MOA error would not be accross the board all the way to 1000 yards and beyond tho, that MOA number is merely a result of the number of MOA needed to dial in for elevation at a given range, and the range itself with a given cant angle to the scope. </p><p></p><p>Any thoughts or corrections. <img src="http://images/icons/smile.gif" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p></blockquote><p></p>
[QUOTE="Brent, post: 28653, member: 99"] Here's a chart at 1000 yards for the 308 win and a 175gr SMK with 12 degrees of rifle cant for comparison. More error is the result of much more MOA needed to zero it at 1000 than the other one. CALIBER: 308 Win MUZZLE VELOCITY: 2600 fps BULLET WEIGHT: 175 gr. BALLISTIC COEFFICIENT: 0.505 SIGHT HT.: 1.76 in. (1.8"/12°) ZEROED AT: 997.9 Yds. INCLINE ANGLE: 0 deg. WIND: 0 mph STANDING TARGET ATMOSPHERE: Std. 300 ft. 59° F./300 ft./29.53 in. HG/78% R.H. 'G1' STANDARD FLAT BASE Range- Vel.- Energy- Drop- Path---- Defl.-- Time- Lead- Yards- fps- Ft.Lbs.- Inches- MOA- Inches- Sec.- Inches- 000 2600 2627 0.00 0.00 -0.37 0.000 0.0 100 2428 2290 2.69 38.49 8.85 0.119 0.0 200 2262 1988 11.29 36.51 18.08 0.247 0.0 300 2102 1717 26.70 33.68 27.30 0.385 0.0 400 1949 1477 49.99 30.39 36.53 0.533 0.0 500 1804 1264 82.44 26.66 45.76 0.693 0.0 600 1666 1079 125.60 22.47 54.98 0.866 0.0 700 1537 918 181.31 17.77 64.21 1.054 0.0 800 1419 782 251.74 12.48 73.44 1.257 0.0 900 1312 669 339.47 6.54 82.66 1.477 0.0 1000 1219 577 447.41 -0.15 91.89 1.714 0.0 TRAJECTORY CROSSES LINE OF SIGHT AT 3.9 & 997.9 yds. PATH IS 141.97 IN. OVER LINE OF SIGHT AT 566.4 yds. After some figuring, I figure that a scope to rifle mounting angle error of 1 degree would equal .01111 MOA windage deflection for every 1 MOA elevation dialed for a farther range beyond the 100yd zero. A 90 degree angle mounting cant error would obviously cause a 1 MOA windage correction if dialing in 1 MOA elevation. Half that cant angle, 45 degrees, would cause .5 MOA deflection and so on. So 1/90th of that is equal to .01111 MOA deflection per 1 MOA elevation dialed in if the scope is canted only 1 degree. So if the "scope" alignment instead is off the same 12 degrees from the rifle when installed, the error at 1000 yards with the 38.61 MOA needed to rezero there, there would be .01111 * 12 * 38.61 * 10 = 51.47" or 4.91 MOA deflection error introduced. That 4.91 MOA error would not be accross the board all the way to 1000 yards and beyond tho, that MOA number is merely a result of the number of MOA needed to dial in for elevation at a given range, and the range itself with a given cant angle to the scope. Any thoughts or corrections. [img]images/icons/smile.gif[/img] [/QUOTE]
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