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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Bullet Drop with a Duplex Reticle???
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<blockquote data-quote="sscoyote" data-source="post: 158962" data-attributes="member: 1133"><p>I also apply plex reticles for downrange zeroing both vertical and horizontal, and rangefinding. The scope that i've used for this recently was a 4-12X Bushnell Banner on a .17 Mach IV XP-100 HG for coyotes mostly. When i was checking loads for this rig, i simply measured the reticle as closely as possible to .1 inch at 100 yds. @ 12X. This rig has an effective range of about 300 yds. or so for coyotes, so the plex post tip subtension @ 12X is enuf for me. Here's how i do it--</p><p></p><p>The plex post tips subtend 2.9 MOA from x-hair axis. Now when i run a ballistics program for my load i see that with a 225 yd. zero my drop for 340 yds. is right at 2.9 MOA. This establishes my lower post tip zero @ 340 yds. (@ 12X). The next thing i do is see what the MOA drop is at even 25 yd. intervals. When i divide each of those values by the total subtension of 2.9 then i get the reference along the reticle for that range in .1 of the total subtension. Do the exact same thing for 10 mph wind as well, and here's what the range sticker looks like--</p><p></p><p>range-elevation-windage.....(P)= point blank range</p><p></p><p>150-P-.6</p><p>200-P-.8</p><p>225-0-.9</p><p>250-P-1</p><p>275-.4-1.1</p><p>300-.6-1.25</p><p>etc.</p><p></p><p>Taking 1 range as an example if i'm presebted with a 300 yd. shot @ a coyote, and my anemometer measures 10 mph avg. wind from 3 o'clock, then i aim 6 tenths of the way down to the plex post tip from center x-hair, and 1.25 "plex units" wind. I killed a coyote with this rig in exactly this scenario 2 winters ago using a different scope (Burris 4-12X Mini) that had a similar plex post tip measurement. </p><p></p><p>Reticle subtension is exactly proportional to maginification. But it's inversely proportional, since as mag. INCREASES reticle subtension DECREASES. Suppose i wanted to calculate a X that would put me dead on @ 500 yds. with that rig. Suppose i looked at the Ball. program, and it calculated a 500 yd. drop of say 5.8 MOA. All u have to do is use an inversely proportional equation to calculate what X the scope must be set on to establish a subtension to post tip of 5.8 MOA-- here's the equation:</p><p></p><p>12X/5.8 = Xx/2.9...... X=6x</p><p></p><p>Now set your scope to 6X, and kill that prairie dog. Of course this is all theoretical, and it'd probably be better to use the above-described systems, but i've found that most scopes are calibrated fairly close for magnification, so this should work. Be fun to try and find out huh??</p><p></p><p>Now here's how the reticle rangefinding works with that reticle for say a 12" back to brisket coyote. I apply what i refer to as the "modified mil-ranging formula." Here it is--</p><p></p><p>tgt. size (inches) x range of reticle subtension measurement (usually 100 yds.) / reticle subtension (inches) / quantity of stadia to stadia "gap" tgt. occupies (tenths of the total gap) = range (yds.)</p><p></p><p>Looks complicated but very easy to apply. For the above scope the post tip to post tip measurement is 6"/100yds.</p><p></p><p>Now just punch the figures into the equation for the 12" coyote, and here's what u get--</p><p></p><p>12" x 100 yds. / 6" / 1.0 (coyote gaps right between the plex post tips) = 200 yds.</p><p></p><p></p><p>Simple huh?? Now finish the rangeing chart for that reticle--</p><p></p><p>12 x 100 / 6 / 0.9 = 220</p><p></p><p>200 / 0.8 = 250</p><p></p><p>200 / .7 = 285</p><p></p><p>200/.6=335</p><p>200/.5 (x-hair) = 400</p><p></p><p>Reticle rangefing is often a good mathematical guess, but it's better than human eyes, that's for sure.</p><p></p><p>This is fun stuff to play with, if nothing else to learn more about your scope/reticles. And it will blow your mind how effective it can be at times.</p></blockquote><p></p>
[QUOTE="sscoyote, post: 158962, member: 1133"] I also apply plex reticles for downrange zeroing both vertical and horizontal, and rangefinding. The scope that i've used for this recently was a 4-12X Bushnell Banner on a .17 Mach IV XP-100 HG for coyotes mostly. When i was checking loads for this rig, i simply measured the reticle as closely as possible to .1 inch at 100 yds. @ 12X. This rig has an effective range of about 300 yds. or so for coyotes, so the plex post tip subtension @ 12X is enuf for me. Here's how i do it-- The plex post tips subtend 2.9 MOA from x-hair axis. Now when i run a ballistics program for my load i see that with a 225 yd. zero my drop for 340 yds. is right at 2.9 MOA. This establishes my lower post tip zero @ 340 yds. (@ 12X). The next thing i do is see what the MOA drop is at even 25 yd. intervals. When i divide each of those values by the total subtension of 2.9 then i get the reference along the reticle for that range in .1 of the total subtension. Do the exact same thing for 10 mph wind as well, and here's what the range sticker looks like-- range-elevation-windage.....(P)= point blank range 150-P-.6 200-P-.8 225-0-.9 250-P-1 275-.4-1.1 300-.6-1.25 etc. Taking 1 range as an example if i'm presebted with a 300 yd. shot @ a coyote, and my anemometer measures 10 mph avg. wind from 3 o'clock, then i aim 6 tenths of the way down to the plex post tip from center x-hair, and 1.25 "plex units" wind. I killed a coyote with this rig in exactly this scenario 2 winters ago using a different scope (Burris 4-12X Mini) that had a similar plex post tip measurement. Reticle subtension is exactly proportional to maginification. But it's inversely proportional, since as mag. INCREASES reticle subtension DECREASES. Suppose i wanted to calculate a X that would put me dead on @ 500 yds. with that rig. Suppose i looked at the Ball. program, and it calculated a 500 yd. drop of say 5.8 MOA. All u have to do is use an inversely proportional equation to calculate what X the scope must be set on to establish a subtension to post tip of 5.8 MOA-- here's the equation: 12X/5.8 = Xx/2.9...... X=6x Now set your scope to 6X, and kill that prairie dog. Of course this is all theoretical, and it'd probably be better to use the above-described systems, but i've found that most scopes are calibrated fairly close for magnification, so this should work. Be fun to try and find out huh?? Now here's how the reticle rangefinding works with that reticle for say a 12" back to brisket coyote. I apply what i refer to as the "modified mil-ranging formula." Here it is-- tgt. size (inches) x range of reticle subtension measurement (usually 100 yds.) / reticle subtension (inches) / quantity of stadia to stadia "gap" tgt. occupies (tenths of the total gap) = range (yds.) Looks complicated but very easy to apply. For the above scope the post tip to post tip measurement is 6"/100yds. Now just punch the figures into the equation for the 12" coyote, and here's what u get-- 12" x 100 yds. / 6" / 1.0 (coyote gaps right between the plex post tips) = 200 yds. Simple huh?? Now finish the rangeing chart for that reticle-- 12 x 100 / 6 / 0.9 = 220 200 / 0.8 = 250 200 / .7 = 285 200/.6=335 200/.5 (x-hair) = 400 Reticle rangefing is often a good mathematical guess, but it's better than human eyes, that's for sure. This is fun stuff to play with, if nothing else to learn more about your scope/reticles. And it will blow your mind how effective it can be at times. [/QUOTE]
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Bullet Drop with a Duplex Reticle???
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