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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Ballistic mil dot question
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<blockquote data-quote="Buffalobob" data-source="post: 70705" data-attributes="member: 8"><p>Cont'd</p><p></p><p>Let us think about how the hashmarks work at different magnification. we will use the 300 yard mark as an example.</p><p></p><p>For 1000 yards</p><p></p><p>Frist two hash marks </p><p></p><p>At 14 power</p><p></p><p>2.4 inches @ 100yds X 1000yds/100yds = 24 inches @ 1000yds</p><p></p><p>At 28 X</p><p></p><p>14/28 = 0.5</p><p></p><p>2.4 inches X 0.5 X 1000/100 = 12 inches</p><p></p><p>At 32 Power</p><p></p><p>14/32 = 0.4375</p><p></p><p>2.4 inches X 0.4375 X 1000yds/100yds = 10.5 inches @ 1000 yds</p><p></p><p></p><p>A 8 X</p><p></p><p>14/8 = 1.75</p><p></p><p>2.4 inches X 1.75 X 1000yds/100yds = 42 inches</p><p></p><p></p><p>What we see here is that at the higher magnification that we would like too make the longer shots the hash marks are not of great use. At lower power they are more use but we will have a harder time with our aiming point because of the low power.</p><p></p><p></p><p>Let us see if we can adapt the hash marks to another bullet </p><p></p><p></p><p>Being as the hash marks are "calibrated at 14" for the 300 Win mag w 150 grain bullet @ 3350fps let us see what happens is we shoot the 220 Sierra Mk at 2700 fps</p><p></p><p>The reticules is calibrated for the following drops from 100 yd zero : 200 = 1.6, 300= 7.3, 400= 18.3, 500= 36.0, 600 = 62.6 for the 150 gr</p><p></p><p>According to Sierra manual the 220SMK for a 100 yds Zero drop at range will be 200 = 3.79, 300= 13.48, 400= 29.77, 500 = 53.45, 600 or = 85.44</p><p>In other words at 600 yds if we use the hash mark at 14 power we will undershoot the target by 85.44 - 62.6 = 22.8 inches. We will miss an elk, we will miss a moose we will miss a buffalo and we might hit an elephant but only wound it and it will stomp on us.</p><p></p><p>Let convert the 220 SMK trajectory to inches adjustment </p><p></p><p>200 = 1.9</p><p>300= 4.49</p><p>400= 7.44</p><p>500= 10.7</p><p>600= 14.26</p><p></p><p>What we want to do is see if there is a power setting that will allow us to use the hash marks with the 220SMK, so let us calculate a ratio of 600 yd adjustments</p><p></p><p>14.26 divided by 10.4 = 1.37 is the ratio</p><p></p><p>14power divided by 1.37 = 10.2 power will be the calibration point .</p><p></p><p>OK then let us compute a table to double check our work</p><p></p><p></p><p>0 =0</p><p>200yd=0.8 X 1.37 = 1.096</p><p>300yd=2.4 X 1.37 =3.28</p><p>400yd=4.6 X 1.37 = 6.3</p><p>500yd=7.2 X 1.37 =9.86</p><p>600yd=10.4 X 1.37 =14.25</p><p></p><p>What we see is that by using the ratio at 600 yds we get a good match at 600 yds but at 200 yds we will shoot 2 inches too low and at three hundred yards we will shoot 3 inches too low and at 400 yards we will shoot 4.4 inches low and at 500 yds we will be 4 inches low. Now then if we choose to run the ratio at 500 yards instead of 600 yds the following will happen</p><p></p><p>10.7 divided by 7.2 = 1.49</p><p></p><p>14 power divided by 1.49 = 9.4 power calibration point</p><p></p><p>200yd=0.8 X 1.49 = 1.19</p><p>300yd=2.4 X 1.49 = 3.58</p><p>400yd=4.6 X 1.49 = 6.85</p><p>500yd=7.2 X 1.49 =10.7</p><p>600yd=10.4 X 1.49 =15.5</p><p></p><p>At 200 yds we will be 1.4 inches low, at 300 we will be 2.2 inches low, at 400 we will be 2.4 inches low, at 500 we will be dead on and at 600 yds we will be 7.2 inches high. This is not good to be 7 inches high so we can see it is better to run ratios at 600 yards than 50 yards.</p><p></p><p>Now then as we all understand scope manufacturers round off their numbers and when they say the calibration point is about 14 power we do not know what that means. It could be 14.3 which would start to change the calculations.</p><p></p><p>Now then I hope you are not too confused with all of thess calculations and if you had a different question in mind than just ask it again differently.</p></blockquote><p></p>
[QUOTE="Buffalobob, post: 70705, member: 8"] Cont'd Let us think about how the hashmarks work at different magnification. we will use the 300 yard mark as an example. For 1000 yards Frist two hash marks At 14 power 2.4 inches @ 100yds X 1000yds/100yds = 24 inches @ 1000yds At 28 X 14/28 = 0.5 2.4 inches X 0.5 X 1000/100 = 12 inches At 32 Power 14/32 = 0.4375 2.4 inches X 0.4375 X 1000yds/100yds = 10.5 inches @ 1000 yds A 8 X 14/8 = 1.75 2.4 inches X 1.75 X 1000yds/100yds = 42 inches What we see here is that at the higher magnification that we would like too make the longer shots the hash marks are not of great use. At lower power they are more use but we will have a harder time with our aiming point because of the low power. Let us see if we can adapt the hash marks to another bullet Being as the hash marks are “calibrated at 14” for the 300 Win mag w 150 grain bullet @ 3350fps let us see what happens is we shoot the 220 Sierra Mk at 2700 fps The reticules is calibrated for the following drops from 100 yd zero : 200 = 1.6, 300= 7.3, 400= 18.3, 500= 36.0, 600 = 62.6 for the 150 gr According to Sierra manual the 220SMK for a 100 yds Zero drop at range will be 200 = 3.79, 300= 13.48, 400= 29.77, 500 = 53.45, 600 or = 85.44 In other words at 600 yds if we use the hash mark at 14 power we will undershoot the target by 85.44 - 62.6 = 22.8 inches. We will miss an elk, we will miss a moose we will miss a buffalo and we might hit an elephant but only wound it and it will stomp on us. Let convert the 220 SMK trajectory to inches adjustment 200 = 1.9 300= 4.49 400= 7.44 500= 10.7 600= 14.26 What we want to do is see if there is a power setting that will allow us to use the hash marks with the 220SMK, so let us calculate a ratio of 600 yd adjustments 14.26 divided by 10.4 = 1.37 is the ratio 14power divided by 1.37 = 10.2 power will be the calibration point . OK then let us compute a table to double check our work 0 =0 200yd=0.8 X 1.37 = 1.096 300yd=2.4 X 1.37 =3.28 400yd=4.6 X 1.37 = 6.3 500yd=7.2 X 1.37 =9.86 600yd=10.4 X 1.37 =14.25 What we see is that by using the ratio at 600 yds we get a good match at 600 yds but at 200 yds we will shoot 2 inches too low and at three hundred yards we will shoot 3 inches too low and at 400 yards we will shoot 4.4 inches low and at 500 yds we will be 4 inches low. Now then if we choose to run the ratio at 500 yards instead of 600 yds the following will happen 10.7 divided by 7.2 = 1.49 14 power divided by 1.49 = 9.4 power calibration point 200yd=0.8 X 1.49 = 1.19 300yd=2.4 X 1.49 = 3.58 400yd=4.6 X 1.49 = 6.85 500yd=7.2 X 1.49 =10.7 600yd=10.4 X 1.49 =15.5 At 200 yds we will be 1.4 inches low, at 300 we will be 2.2 inches low, at 400 we will be 2.4 inches low, at 500 we will be dead on and at 600 yds we will be 7.2 inches high. This is not good to be 7 inches high so we can see it is better to run ratios at 600 yards than 50 yards. Now then as we all understand scope manufacturers round off their numbers and when they say the calibration point is about 14 power we do not know what that means. It could be 14.3 which would start to change the calculations. Now then I hope you are not too confused with all of thess calculations and if you had a different question in mind than just ask it again differently. [/QUOTE]
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