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Range estimation with a duplex?
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<blockquote data-quote="sscoyote" data-source="post: 6564" data-attributes="member: 1133"><p>Had a question about the use of plex reticle for second zero reference from Vic in MT (sorry Vic had a computer or maybe computer user glitch and lost it). Here is what i've come up with from my research. I've created a plex reticle worksheet that can be used to calculate a rangefinding system and additional zero's for any plex reticle. At exactly 102 yds, from the kitchen table out my front window is a sign post with holes along it that measure exactly 1" apart. This provides a quick and simple measurement of the reticle subtension. When a friend comes over we set his gun up on bags on the kitchen table ( when the wife's not home) to measure the reticle (at the scopes highest mag.). As soon as i obtain the mearurement i write it on a sticker and put it on the inside of the turret cover for future reference if needed. If he knows the m.v. of his load i then follow the following calculations to maximize the potential of the reticle.</p><p>1) Run the loads ballistics figures through Exbal (or any other ballistics program) to determine the maximum point blank range (MPBR) of the intended target.</p><p>2) Then calculate the mag. needed for MPBR for rangefinding purposes using the following LINEAR formula: highest scope mag./ target measurement= X mag./reticle subtension @ highest scope mag. @ MPBR. Now this means that when you adjust the scope to this calculated (X) mag. when the target subtends the reticle or is bigger, just aim dead center and shoot for a certain (theoretically) hit. Now here's the nice little additional feature that one may wish to adopt. Suppose the rangefinding mag. needed on a 4-12X scope is 5.5X. well i don't know about you guys but when i'm presented with the opportunity (time actually) to use this system, i want the highest mag. i can get for a calculated shot-- right? So instead of using the center x-hair- post gap for rangefinding try using 2X that mearurement (11X in this case) for the post-post gap instead. This should provide a higher mag. for rangefinding purposes, as well as additional reference (the center x-hair) for approximating range at longer distances. </p><p>3) Now in order to calculate the new 100 yd. subtensions for bottom post zero @ MPBR mag. apply the following formula: X" @ 100 yds. @ MPBR mag./highest scope mag.= subtension @ highest scope mag. @ 100 yds./scope mag. @ MPBR. From here i use Exbal to calculate the new zero for the lower post (at the mag. needed for MPBR rangefinding). I can also punch in 2X that measurement for an aditional zero (in this case suppose that zero range is 625 yds. If i've calculated this distance to the target simply hold the lower post on the target, note where the x-hair is then bring the lower post to that spot and shoot--- theoretically, mind you). trying to create a mathematical model for this calculation is no longer linear and requires algebraic formulas since the bullet trajectory is parabolic in nature. </p><p></p><p>Of course, this is all theoretical since i just thunk it up recently, but it should work (check my calculations please administrators) since the relationship between reticle subtension, apparent image size and scope magnification is linear, and should at least get you on paper, and while you're testing this mathematical model it might be a good idea to check to make sure the MPBR for rangefinding is right also. The nice thing about this system is that it can save time and wasted bullets at the range.</p><p></p><p></p><p>Sounds like Old Timer's got the system down to a science as well-- even more since he appears to be using his upper post as the original zero for MPBR.</p><p></p><p>[ 08-21-2003: Message edited by: sscoyote ]</p><p></p><p>[ 08-22-2003: Message edited by: sscoyote ]</p><p></p><p>[ 08-22-2003: Message edited by: sscoyote ]</p><p></p><p>[ 08-22-2003: Message edited by: sscoyote ]</p><p></p><p>[ 08-22-2003: Message edited by: sscoyote ]</p></blockquote><p></p>
[QUOTE="sscoyote, post: 6564, member: 1133"] Had a question about the use of plex reticle for second zero reference from Vic in MT (sorry Vic had a computer or maybe computer user glitch and lost it). Here is what i've come up with from my research. I've created a plex reticle worksheet that can be used to calculate a rangefinding system and additional zero's for any plex reticle. At exactly 102 yds, from the kitchen table out my front window is a sign post with holes along it that measure exactly 1" apart. This provides a quick and simple measurement of the reticle subtension. When a friend comes over we set his gun up on bags on the kitchen table ( when the wife's not home) to measure the reticle (at the scopes highest mag.). As soon as i obtain the mearurement i write it on a sticker and put it on the inside of the turret cover for future reference if needed. If he knows the m.v. of his load i then follow the following calculations to maximize the potential of the reticle. 1) Run the loads ballistics figures through Exbal (or any other ballistics program) to determine the maximum point blank range (MPBR) of the intended target. 2) Then calculate the mag. needed for MPBR for rangefinding purposes using the following LINEAR formula: highest scope mag./ target measurement= X mag./reticle subtension @ highest scope mag. @ MPBR. Now this means that when you adjust the scope to this calculated (X) mag. when the target subtends the reticle or is bigger, just aim dead center and shoot for a certain (theoretically) hit. Now here's the nice little additional feature that one may wish to adopt. Suppose the rangefinding mag. needed on a 4-12X scope is 5.5X. well i don't know about you guys but when i'm presented with the opportunity (time actually) to use this system, i want the highest mag. i can get for a calculated shot-- right? So instead of using the center x-hair- post gap for rangefinding try using 2X that mearurement (11X in this case) for the post-post gap instead. This should provide a higher mag. for rangefinding purposes, as well as additional reference (the center x-hair) for approximating range at longer distances. 3) Now in order to calculate the new 100 yd. subtensions for bottom post zero @ MPBR mag. apply the following formula: X" @ 100 yds. @ MPBR mag./highest scope mag.= subtension @ highest scope mag. @ 100 yds./scope mag. @ MPBR. From here i use Exbal to calculate the new zero for the lower post (at the mag. needed for MPBR rangefinding). I can also punch in 2X that measurement for an aditional zero (in this case suppose that zero range is 625 yds. If i've calculated this distance to the target simply hold the lower post on the target, note where the x-hair is then bring the lower post to that spot and shoot--- theoretically, mind you). trying to create a mathematical model for this calculation is no longer linear and requires algebraic formulas since the bullet trajectory is parabolic in nature. Of course, this is all theoretical since i just thunk it up recently, but it should work (check my calculations please administrators) since the relationship between reticle subtension, apparent image size and scope magnification is linear, and should at least get you on paper, and while you're testing this mathematical model it might be a good idea to check to make sure the MPBR for rangefinding is right also. The nice thing about this system is that it can save time and wasted bullets at the range. Sounds like Old Timer's got the system down to a science as well-- even more since he appears to be using his upper post as the original zero for MPBR. [ 08-21-2003: Message edited by: sscoyote ] [ 08-22-2003: Message edited by: sscoyote ] [ 08-22-2003: Message edited by: sscoyote ] [ 08-22-2003: Message edited by: sscoyote ] [ 08-22-2003: Message edited by: sscoyote ] [/QUOTE]
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