Home Forums Hunting & Shooting Hunting Optics using duplex reticle for bullet drop

ss: Good posts! Informative....

I was driving home from bass fishing last night,thinking about this stuff and for me anyway, I started thinking about the realities of shooting BG animals....

In these times,with increased emphasis on new sighting technology,I hear reference made to the holdover methods as "guessing",and I suppose when a scope behaves precisely the way it should,clicking up can be a very precise way to hit a small target at long range, if the distance is known.

But on a hunt, in backcountry,after a rifle has been banged around by a week or 10 days of hunting,and has traveled a few thousand miles to higher elevations,(to say nothing of the accumulated wear and tear on the scope resulting from the several thousand rounds to learn the system)etc.and I have a bull elk or whatever in my sights at 400 yards,know my rifle to the "T" at that distance,I would not even THINK about dialing ANYTHING "in"....gravity is constant; little tiny springs in a mechanical system (which may not work the way they are supposed to) could be a lot less so.

I'm going to trust what's between my ears and a rifle of known consistent zero that I have shot a lot to determine drop at various distances,rather than a mechanical system that may go "bonkers" at the wrong time.....if this brands me as a hide-bound reactionary, so be it.I have been around enough rifle scopes in my life that the only one's I REALLY trust are solidly mounted fixed powers....if someone told me to start clicking in the presence of game, I'd need a sedative....

To me,dots and hash marks are preferable because the rifle's zero does not change;it's a refinement of hold over,and if it "only" gets you to 500 or 600 yards,so be it. I don't belong to the "if I can see it,I can hit it" school of BG hunting.

As to "guessing", I can only assume that those who believe this stuff have spent more time at the range than actually hunting big game; 10"-25 " of drop is the same whether you compensate for it by clicking up,using a dot,or imposing your reticle against the side of an animal whose dimensions you know and understand.

On those rare occaisions when I have had to hold at the top of an animals back, or higher, to kill him, I knew the result before the hammer fell.A few 10,000 rounds of expended ammo in practice assured the outcome.

And as I think back on those situations,had a I started clicking,by the time I was ready,those animals would likely have been gone.I'll put my money on a flat shooting rifle and and a solid scope(whose zero stays in one place) any day.YMMV

... like a .270 with a 4x Leupy ?



Could see the logic in that. Hope you got some bass.

I couldn't agree more. I taught my son the same thing with his 7-08, and like youm BobinNH we don't worry too much about anything at sensible distance other than if he's big enough. My nephew uses his 7mag the same way. I can't tell you how many things have died in these wide open W TX spaces using this setup. It's simple, that's why I like it, and why I'm a big believer in the "3" high at 100 club".

cmg: uhh,yes ...among others

On the bass...I did manage to scrape up a few!

Exactly. "There may not be much time when he stops". Or, even worse, when he finally shows himself in the clear and keeps moving.
I've used the simple duplex. I've used various dial setups, and I've used stuff like the Mil-Dot. For my uses, keeping in mind that I hunt everything from very wide open spaces, to very heavy cover, the basic duplex, with a known opening width, works the best under all of these conditions. I tend to favor the 6X Leupolds over the 4X models because they allow me to see a little better when it comes to seeing twigs at ranges over 75 yds. etc., in the way of my shot.
As far as bullet drop goes, I've had more trouble over shooting stuff, again shooting in a hurry at say 150-200 yds., than not holding high enough at the longer ranges. As long as you know where to hold the reticle, you're good.
Once you get beyond such "crude methods," you have lots of other things that factor in. Wind for one. That's why conditions have to be "ideal" for me to consider anything over 350, maybe 400, yds. E

Bob, once again I totally agree, I really tried to wring out the Shepherd route as to eliminate a rangefinder,to busy with poor light and most of my bigger bucks have been taken early or late which translates to low light, in fact even the ballistic plex style holdover marks get hard to see as well when that big brute steps out with a few minutes of light left,Spent a few bucks on turrets etc, and yes they do work, prolly the cats azz for t-lopes etc,

Dakota: Can't comment on the LR reticles in low light because I have used Duplex.I have sat fields in Alberta and watched the lights go out.Made up my mind that the darker it gets, the closed he's gonna have to be before I'd take the shot.If they get back into the bush, it would be no fun trying to find him in the dark;and I don't want to sacrifice my animal to wolves or coyotes by waiting till morning to shag him.

The reality is that with the best binoculars by Zeiss,Leica and Swaro(yes I've used them all),it can be hard to distinguish horns from background bush and judge him anyway at last light;I am not going to blast away unless a)he's what I came for,and b)I'm certain I can kill him.
What I'm saying is a lot of times, long range and last light frequently don't mix too well

Interestingly, all this rangefinding (and downrange zeroing) with reticles and/or turrets is based on a slight moification of the mil-ranging formula, whether it's Leatherwood, plex, mil-dot, turret clicks, whatever. All that's necessary is to replace the 3.6 inch per hundred yds. subtension with whatever subtension u may be using. I actually stumbled on this concept years ago while studying the mil-dot system. I kept on seeing the number 27.8 turn up in the equation. I figured it was a factor of some sort, but i didn't know where it came from. When i finally figured out that it was just the ratio of range to subtension (100 yds. / 3.6" = 27.8) i thought why wouldn't a simple plex work equally as well. Well turns out it does, and often better than the mil-dot as long as the subtension is smaller than 3.6 IPHY it would have to be more accurate. Just this last winter a buddy and i were out hunting coyotes and while taking a break at an old homestead a herd of antelope were out milling around on a hillside. My buddy had a 4.5-14x VX-III on top his rig so i asked him to gap the buck in his Duplex at 14x. He did so and told me 1.1 "1/2 plex units". I already knew the subtension was 2.7 IPHY X-post tip. The buck was lasered at right around 495 yds. So i plugged it into the equation figuring 15" back to brisket-- 15x100/2.7/1.1= 505. We about fell over--couldn't believe it. After awhile they moved out to a lasered 700. He did it again and siad about 80% (0.8). So once again--15x100/2.7/.8=694. This time we did fall over.

Of course a complete understanding of the mil-ranging formula will show just how lucky we were at the 700-yd. mark.

The 6x FX-II or III have a perfect subtension for big game at 9 IPHY post tip to post tip. A very simple chart could easily be made for any big game spp.

Learned that several years ago trying to bracket a coyote just before dark with a 6-24x Burris Signature. That was an exercise in futility i can sure tell ya'.

sscoyote: Near as I can tell the standard Leup reticle on a 6X subtends 5" at 100 yards;at least that's what I have been using, and it has worked pretty well to 500 for me with the faster cartridges(300 Weatherby,7 mags, etc).

Bob, i got that info from the current catalog (9.0 IPHY plex post tip to plex post tip--4.5 for X-PPT). It may be different for other years.

The Leupold 6x bottom picket is 18" low at 400 yards. That corresponds almost perfectly to the brisket of a big deer and the drop of most -06 class cartridges.

It works as an instant rangefinder also--if the deer fills the gap plus extra, then hold on hair and shoot. If he just fills it, then the bottom picket is your dead-on hold. If he doesn't fill the space, it usually means I have to get closer.

I have an older, M8 6X42 with a Medium Duplex, a new conversion of an older M8, 6X42 to a Heavy Duplex and the latest FX3 w/ Heavy Duplex. All of them have a measured 9 inch opening between the heavy sections of the reticle. E

E,Coyote,Dakota: OK, it actually subtends a bit less than 5" at 100 yards,and I have been using 5",which is likely why I am a bit low at 500 with the 7mmDakota and 300 Weatherby. This makes sense.

BTW, I am not enough low that I would fail to kill anything...just fractions. Thanks to all.

Sscoyote: I do not follow your equation/ratio wherein you equate 100 yards to 3.6" ("ratio of range to subtension") - shouldn't your ratio compare (make an equation of?) inches to inches and not yards to inches?
In other words 3,600" (100 yards as expressed in inches) to 3.6" or 1,000 to 1.
I am confused on the ratio correlation you are trying to inform us (me!) on.
Could you please try again?
Hold into the wind
VarmintGuy

VG, if u use inches over inches the final answer will not have the units in yds. The mil-ranging formula in it's most basic form is (inches to yards)--

tgt. size (") x range of reticle subtension measurement (yds.) / reticle subtension (") / quantity of gap tgt. occupies (unitless factor) = range (yds.)

so using units only here's the equation--

" x yds. / " = yds.

inches cancels and you're left with yds. = yds.

A milliradian is simply 1/1000th of a radian of a circle. If that angular measurement is stretched to 100 yds. it measures 3.6". In the mil-ranging formula the 27.8 factor is the range of reticle subtension measurement to the reticle subtension itself or in the case of the milliradian it's 100/3.6 (or in the case u point out it's 1000/36"--simply the same factor increased by a factor of 10 or still 27.8 yds./").

Everybody wants to equate the mil-ranging formula to a certain measurement at a certain distance between 2 points vs. what it is at 1000x that distance. But that has no significance really. Any measurement at 1 yd. will be 1000 x that at 1000 yds.-- a plex reticle subtension, archery sight pin measurement, whatever 2 points u may be using (that's the beauty of it all really, that few seem to have figured out. The flexibility of the mil-ranging formula is WAAAYYY bigger than the mil-dot itself. I got lucky and just stumbled upon it 1 day while studying the mil-ranging formula).

So let's adapt the mil-ranging formula using the 18" at 400 yds. DD mentions above for the 9.0 IPHY 6x Leupold Duplex reticle subtension plex post tip to plex post tip (use it just like the mil-dot reticle). Applying the equation above we have this--

18" x 100 yds. / 9.0 / 1.0 (target occupies right at 100% of the PPT-PPT gap) = 200 yds.

...now if it occupies an estimated 90% of it, the decimal equivalent is 0.9 right? Now substitute that into the equation like this--

18x100/9.0/0.9=222

...it should be easy to see that18x100/9.0 is a constant of 200 so just finish the MMRF (modified mil-ranging formula) for the rest of the interpolation--

200/.8=250
.7=285
.6=325
.5=400 (deer now fits between x-hair and plex post tip like DD described above)
.4=500

a couple things should be seen here. x-hair to plex post tip (0.5 of our subtension unit) is about as far as we could expect to go with any degree of accuracy really, because 0.1 less subtension unit nets 100 yds. of range and it gets geometrically more difficult to try and guess an accurate range the further we go (especially on a live target that may not fit that 18" std. perfectly).

Another thing that should be noticed si the point blank range rangefinding system here. Suppose we know that 300 yds. is our max. PBR for whatever load we're using for 3/4ths of a 10" vital zone (what i use). That would be about .7 SU or very close to it, right? So here's what the range sticker would look like on my rig--

P-0.7 PPTs

1.0-200
0.9-225
0.8-250
0.7-285
0.6-325
0.5-400

see how it works?


Calculating bullet drop is also based on the mil-ranging formula since if u think about it a bullet drop at any range is the same type of dimension as a tgt. size when referenced with an optic. Suppose u wanna find out how many MOA constitutes 53.6" drop at 678 yds. Here it is (remember 1.0472" / 100 yds. for MOA)--

53.6 x 100 / 1.0472 / x = 678
x=7.55 MOA

see how that 1 works?

Suppose u sighted whatever that rig is in for the upper plex post tip at whatever range, and your dope called for that drop. U already know that the lower plex post tip is 8.6 MOA (9.0 IPHY converted to MOA). Now just divide 7.55 into 8.6 and u get-0.9. So aim 9 tenths the way down to the lower PPT and see if u don't come mighty close to that chuck...on the 1st shot. I'd bet dollars to donuts u'd get closer than anyone else shooting a 6x scope with no system (Kentucky windage).

See how all this crap comes together?

Crap,

Now I need a degree in Calculus to go deer hunting. I hope the deer stands there long enough for me to get my slide rule out.

If I found myself in the woods with a rifle, a deer, and a slide rule, I would have a hard time deciding whether to shoot the deer or the slide rule.

I'll paraphrase a famous gunwriter;"...the best rangefinder in the world is a rifle chambered for a flat-shooting cartridge..."


I think about this stuff, too,but I am continuously amazed at how much thought and print,anguish,and concern goes into shooting at distances where we have to worry about bullet drop at long range,when probably 90%+ of big game is dropped inside 250 yards....

Bob, this is exactly why I like reticles. Ranging ones I mean. Completely agreed on the simplicity of "no moving parts" for practical hunting ranges. Zero it, verify it, bang it around for years while verifying that it holds zero... and then TRUST IT in a way you can never ever trust a scope that you are dialing all over the place.

(That comes from someone who also likes turrets, but... you know... )

You got more ability or balls or... something than me though, using a plain reticle and holding over. That just doesn't work so well for me. Something like the B&C is WAY far better. For me.