Ranging game with mil dots

Discussion in 'Long Range Scopes and Other Optics' started by moosehunter, Aug 19, 2007.

  1. moosehunter

    moosehunter Well-Known Member

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    Just picked up a mil dot scope. After learning how to use them its apparent how important it is to know the size of the target your shooting at. I would assume the chest cavity would be the best thing on a game animal to range at. Anyone with experience in doing this have any advise to give? Yes I know a laser range finder is the way to go but thats not the way I went. Is there a site that shows fairly accurate, avg. measurements of game?
     
  2. 300rum

    300rum Well-Known Member

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    Hi Moosehunter,
    Yes you are right= You have to range the chest cavity.
    The standard sizes for adult game are:
    Black Bear - 18 inches
    Muley, White Tail Deer - 18 inches
    Sheep - 24 Inches
    Elk, Moose - 34 inches

    BUT RIMEMBER - THE SIZE IS FOR AVERAGE GAME CHEST CAVITY, SO YOU CAN BE WRONG.
    Over all you will be on the target all the time with +/- 25-35 yards at 700-800yards.
    If you are using a MILDOT MASTER you can get on game without problems.
    Mildot Master

    If you go to this location, and read and folow the online class plus try to play with the demo version online of the mildot you will get used with mildot scopes.

    ShooterReady

    REMEMBER ALL THE TIME - USE FOR RANGING THE SCOPE TO THE FACTORY CALIBRATED ZOOM POWER.
    WHEN YOU ARE APPLYING MILDOT RANGING USE THE SAME POWER. DO NOT SWITCH BECAUSE YOU WILL MISS BIG TIME.

    Hope this one gives you one ideea about mildot.
    Chris
     
    Last edited: Aug 19, 2007

  3. Len Backus

    Len Backus Administrator Staff Member

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    Let me play devil's advocate here. I have absolutely no experience in ranging animals with a reticle. But I have often wondered.

    What happens at 500 to 700 yards or so, if the animal's chest dimension is actually 10% more (or less) in vertical dimension than you assume it is? Or what happens if in your excitement (or poor light) you judge the size of the animals chest correctly (not likely), but you mis-read the subtension of the reticle by 10 percent?

    Can someone please run the math and tell me where the bullet impacts?
     
  4. sscoyote

    sscoyote Well-Known Member

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    Good question Len. This is where reverse "milling" helps to understand the error that can be expected from the system. OK, suppose u're using the TMR reticle that has super-fine ranging stadia at .2 mil (.72 IPHY). You're hunting antelope in WY, and u've snuck up to the edge of a shallow basin, and there the big 1 stands way out there (assume 15" back to brisket for a buck according to the Kahles website). Now at 500 yds. he would bracket 4.2 subtension units--

    15 x 100 / .72 / X = 500
    X= 4.2

    Now suppose u're +/- .1 subtension units off with that reticle. Here's the range of error--

    4.1 = 508 yds.

    4.3 = 484 yds.

    miss or hit?? Depends on the cartridge assuming a 10" vital zone (pg. 105 of Bob Hagel's "...Game Loads and Practical ballistic for the Amer. Hunter--great book, BTW, IMO). Of course u're aiming dead center on his chest, so that means +/- 5".

    OK, now he's +/- 1" chest depth measurement @ 4.2 subtension units--

    14 x 100 / .72 / 4.2 = 463 yds.
    16 x 100 / .72 / 4.2 = 530 yds.

    ...so???

    700 YDS. =

    15 x 100 / .72 / X = 700

    X = 3.0 SU's

    15 x 100 / .72 / 2.9 = 718
    15 x 100 / .72 / 3.1 = 672

    14 x 100 / .72 / 3.0 = 648
    16 x 100 / .72 / 3.0 =741

    ...so???

    It's my opinion that any subtension unit has an interpolative accuracy of .1 of it's total subtension--

    TMR = .1 x .72 IPHY = .072 IPHY accuracy
    MD = .1 x 3.6 IPHY = .36 IPHY accuracy

    This is why i like the finer stadia, as it does help somewhat.

    Now, how important that is for big game depends on the individual to make that decision--for a coyote or chuck tho., at least for me i don't really care. I'll hurl 1 his way.
     
    Last edited: Aug 20, 2007
  5. sscoyote

    sscoyote Well-Known Member

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    Let's take a look at the mil-dot since it's so popular-- same calcs.

    15 x 100 / 3.6 / X = 500
    X= .8 SU

    416.6/.9 = 463
    416.6/.7 = 595

    That's a big difference seems to me

    OK. now changing tgt. size by 1" =

    14 x 100 / 3.6 / .8 = 486
    16 x 100 / 3.6 / .8 = 555

    ...so??? once again

    Interestingly tho as u can see with the finer reticle subtension (TMR) error in tgt. size is more important, and with the MD itself interpolating is more important-- which seems logical to me.
     
    Last edited: Aug 20, 2007
  6. sscoyote

    sscoyote Well-Known Member

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    Alright here's something kinda interesting. Finally found my notes on reticle-rangefinding antelope while out coyote hunting last season. Here's 2 measurements that i made with my 4-12X Burris Compact plex reticle that subtends 2.85 IPHY according to the Burris website.

    1) 420 lasered = 1.2 subtension units bracketed back to brisket. Assuming 14" b-b then--

    14 x 100 / 2.85 / 1.2 = 410 (pretty good since i was attempting to interpolate beyond the plex post tips).

    2) 725 lasered = 0.7 subtension units bracketed--

    14 x 100 / 2.85 / 0.7 = 702

    Since mil-dot SU = 3.6 IPHY, i'm assuming that these measurements would be fairly close to what i obtained from my plex reticle system.
     
  7. Buffalobob

    Buffalobob Writers Guild

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    The are a couple of things that take a lot of practice.

    First is where is the top of the animal and where is the brisket. Fur covered creatures have fur and even though that should be obvious, it is important to decide and practice on where the stadia sits in the midst of that fur.

    Secondly, an animal's back is not flat and you have to pick a place and measure it and finally you can't be ranging an uncooperative animal. If it won't turn and give you the correct angle and clear view to measure then you can't get a good distance calculation and you shouldn't shoot.


    Thirdly, You should practice your ranging on a known size object and make sure that the scope actually delivers what the manufacturer says it delivers. This is really critical to check the scope calibration and get your eye used to getting things lined up properly.


    Fourthly, the gun has to be perfectly still so the scope is not wriggling around and so does the animal. Ranging an animal requires just as precise a sight picture as the shooting.

    Fiftly, ranging an isolated animal such as an antelope in short sage brush is a highly questionable activity. I greatly prefer to have other animals around so I can get an indication of "relative body size". Even if you are hunting bucks and bulls it is extremely important to know the does and cows measurements so you can range several of them as well as your intended target. If there are several does around and you keep getting consistent reading off of them and the buck is a different range reading you have to stop and think about the buck's body size and how it is affecting your range calculation. A young spike elk requires a different calculation than a mature bull and different from a cow. For my best ever shot, I even turned the gun sideways and ranged a couple of quaking aspen trees because I knew their trunk diameter. Before I ever pulled the trigger, I had ranged three animals individually and repeatedly and two trees and concluded that the shot would be 1100 yards.

    Finally, for the really long range difficult shots, you need to repeat your ranging technique several times and ensure you are getting a repeatable measurement.

    The whole process takes me about 5- 10 minutes because the animal(s) move around and you have to have the gun perfectly still and lined up properly and you have to rest your eyes, etc.
     
    Last edited: Aug 20, 2007
  8. Buffalobob

    Buffalobob Writers Guild

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    I would just add for those of you who don't understand what I said about the need to practice ranging on live animals, you should go up above in the Forum to "Lens Nature Photography" and look at those two bulls.

    On the elk on the left side, where would you place the stadia on his back. Once you decide the location, look at his fur and decide where the stadia is going to actually be placed.

    On the elk on the right, the guy has a brisket that is not level. He has been drinking too much beer. If you are laying out past 1K with your rifle where you cannot afford errors, then you have to pass or wait until he gets still and changes position. Also look at the fur on his backbone, the guy didn't comb his hair and it is all over the place. You have to anticipate this and have a system of placing the stadia in a set and established manner.

    If you look at the two elk, one has more body depth than the other. Which one is the regular elk and which one is the midget elk?
     
  9. moosehunter

    moosehunter Well-Known Member

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    Absolutely practise is the key. I'll run the math with the 18" and the 34" to see how far out a margin of error would still allow a good hit and call that my max distance.