Bullet Drop with a Duplex Reticle???

Discussion in 'Long Range Scopes and Other Optics' started by DEVO, Jun 26, 2007.

  1. DEVO

    DEVO Member

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    Hello all, I am trying to locate a thread here that showed how an individual used his scopes power settings to first range the target (Duplex) and then again uses his scopes power setting to set his lower transition (thin hair becomes thick)as his point of aim therefor adjusting for the bullet drop. The idea seems very interesting, and I would like to mess around with the idea (most likely on an air rifle). I tried searching for this topic, but no luck what so ever.

    Thank you all in advance.
     
  2. mongoose

    mongoose Well-Known Member

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    I believe you can use the distance between the cross hair and the duplex to estimate range and adjust for drop based on the range.

    Not sure about other scopes but mine gives an accurate reading at 10x anything else is guestimation.

    Hope this helps.
     

  3. MachV

    MachV Well-Known Member

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    I don't use the duplex for ranging, got other tools for that. Heck you gotta have a range finder to figure out the scope settings anyway. For me the problem with ranging is am I looking at a pup or a full grown prairie dog?
    Using the duplex for bullet drops is fairly easy though...for short range work! Firsts off you will need 100 yards and a target with MOA grids, inch grids will work too.
    For me I adjust the power to give me 2 MOA between the x hair and transition to keep it simple. Always turn power all the way up and then down to the aliening marks you put on the scope for 2MOA=double check! With this setup you have a poormans R-2 reticle set up for zero(top transition), 2MOA(x hair) and 4MOA(bottom transition).
    The only duplexes I have left are on 3 12x Leupold's,They are already set to 2MOA and always have ben. Most of my targets are prairie dogs or jack rabbits. For the 204 shooting 40grain Vmaxes @ 3750fps this allows the top to be zero, the Xhairs to be 285 yards, the bottom to be 400 yards. A little guesswork is required for the space in between the three points but it gives you a good guide line.
    I use the same system to turn the 6-24 IOR scopes into MOA hashes instead of ½ mills, all you do is turn the power down from 24x to 18x.
    Just about any variable scope can be adjusted to read whatever you get used to but for me MOA is the easiest to convert ALL scopes to and 2 MOA seams to work best.
     
  4. DEVO

    DEVO Member

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    Mach V, very close to what I was trying to get at, but still very useful. For ranging I do use a range finder. I ideally would like to sight in my rifle at 300 yards (X @ 10 power), therefore the margin of human error will be minimized. So if I want to shoot to 500 yards, I can zoom in to 12 power and use the lower (transitional) area as the aim point. And if I need to shoot with-in 150 yards, I can zoom out to 6 power and use the lower (transitional) area. Of course all this requires a good evaluation of the reticle. I need to find an accurate way of finding out what is the distance between the THICK hairs.... 36" @ 10X or 30" @ 12X...etc...
     
  5. Buffalobob

    Buffalobob Writers Guild

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    Take a large Box, board or other thing and use some blue painters tape to stripe it every two or three inches. Set it at exactly 100 yards. Lay your rifle in a good rest. Get you a pencil and piece of paper. At every power setting record the distance enclosed between the duplex observed on the marked board.

    To translate these distances measured at 100 yards to 200 yards just multipley by two and for 300 yards multiply by 3 and so forth. For wierd distances such as 473 yards multiply by 4.73.

    When you are finished you will have a big sheet of paper with yardages going along one edge and powers along the other and in all the little boxes in between will be the inches of drop.

    Now then, if you understand what I have just typed you are lucky not to be confined to an institution where a lot of people wear white coats. It is just a maater of time before they catch you. /ubbthreads/images/graemlins/grin.gif
     
  6. DEVO

    DEVO Member

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    Thanks Buffalobob... that was the methodology I was thinking of. Thank you all for your input.
     
  7. sscoyote

    sscoyote Well-Known Member

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    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.
     
  8. DEVO

    DEVO Member

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    Wow SScoyote,
    You really broke it down very well. I think I'm going to try your method (all methods) on my air rifle first; just to see if I can UNDERSTAND and milipulate the scope powers. It's funny how the longer shot you want to make the less power you'll use and the smaller the target will be in your scope. I guess that's the limiting factor of this bullet drop method.
     
  9. sscoyote

    sscoyote Well-Known Member

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    Yes, It is funny how that inversely proportional system works. I learned a lot about this some years ago right out the front window of my house actually. The street ran straight away from my window to over 1000 yds. distant. So i took a tape measure and a laser 1 day and measured and lasered all the signs. I wrote down those figures, and i then literally had an optics laboratory established right out the front window. I could then calculate X's i would need to bracket signs between plex post tips. It was really fun, and quite educational. One of the best things about understanding the "mod. mil-ranging formula" is that it allows u to calculate how effective the system is, and a couple other things as well, since it's composed of 5 different variables, any of which can be easily calculated once the other 4 are known. It's really simple mathematics. Here's a link to an article on the web that explains reticle zeroing, and rangefinding that may help. It also includes point blank range rangefinding and rangefinding with ballistic reticles under Item C) Reticle Rangefinding--

    www.ottllc.com/specialtypistols/sp20.pdf

    Nice thing about it is u can order the optics catalogs, from many of the companies that advertise their reticle subtensions. This has been extremely helpful for me, and really the best source of info regarding scopes.

    Couple years ago i was out at a turkey shoot, and we had to shoot a bowling pin at 600 yds. I was using a 3-12X Burris LER Ballistic Plex reticle, that i'd measured the reticle subtension from upper post tip to axis @ 3.1 inch per hundred yds. Before we shot i asked if i could measure the bowling pin. It was 15" tall. When we got to the 600 yd. line i gapped it in my reticle at 0.8 of the abovementioned subtension. So by applying the "MMRF" above here it is--

    15 x 100 / 3.1 / 0.8 = 605 yds.

    Neat, i thought. Later as i got a better grip on the system i then realized just how lucky that was when i started manipulating the formula some.

    1 last thing about this reticle-ranging stuff. I now have a Tactical Milling Reticle in a Leupold scope, that has a very fine system of ranging to the tune of .2 mil stadia. Most guys apply that reticle to an accuracy level of maybe 1/4th of that subtension, since it can get quite complicated trying to divide it into tenths, but once reticle subtension is understood, it can be very easily calculated if the basic ranging unit is .2 mil instead of the std. 1 mil. This stuff is an education, and a fun one for sure.