Bullet drop compensation dials (BDC dials)

Discussion in 'The Basics, Starting Out' started by relabbe, Apr 7, 2006.

  1. relabbe

    relabbe Active Member

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    I have a Leupold VX III 3.5 X 10 50mm and would like to equip it with a BDC dial. I know that leupold custom shop are supplying them but I would like to know if there are other suppliers making them for the leupold? If you know the cost I would also appreciate this information. Thanks René
     
  2. dalefarmer

    dalefarmer Member

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  3. jwp475

    jwp475 Well-Known Member

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    Why not target turrets?
     
  4. relabbe

    relabbe Active Member

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    Thanks Dalefarmer and JWP475, Is there any difference between a BDC and a target turret? I thought there were the same. What is the difference?

    Thanks again,
     
  5. MagMan

    MagMan Well-Known Member

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  6. dalefarmer

    dalefarmer Member

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    I guess just the markings on them.
    From what I have picked up reading this forum, target turrets are better due to changes in things like altitude and temperatures.
     
  7. Bart B

    Bart B Well-Known Member

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    Target turrets are usually marked in minutes of angle divided into fractions (1/8th, 1/4th MOA). These are great because once you have a zero with a given load you can write down what the setting is. As your barrel wears out or you change environment (temperature, altitude), things will change.

    Bullet drop compensators only work accurate when a given load is first used in a new barrel and the compensator is calibrated to exactly what your bullet's trajectory is. Otherwise, the further you are away from the target or atmospheric conditions the compensator was set for, the greater your error will be. The error can easily be as much as a foot or more at 600 yards or 5 feet or more at 1000 yards.

    I favor target turrets; easier to make changes to your written dope sheet or label stuck on your rifle's stock just below the scope so you can see it from a shooting position. And a different dope label/sheet for each load is great.
     
  8. Buffalobob

    Buffalobob Writers Guild

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    Technology has changed and both Brown dog and 4ked horn have written computer programs that will print out custom paste on BDCs.

    You just run your ballistics program and get your drops and then use sideways printing with a small font in either MS Word or excell and print it on to a sticky label and paste it on your target turrets. When you change loads or decide to hunt in a different elevation such as Death Valley you just make yourself a new label and stick it on the target turrets. In theory it is just as accurate a method as the old 3X56 cards or the cheat sheet on the stock.
     
  9. Guest

    Guest Guest

    [ QUOTE ]
    Technology has changed and both Brown dog and 4ked horn have written computer programs that will print out custom paste on BDCs.

    You just run your ballistics program and get your drops and then use sideways printing with a small font in either MS Word or excell and print it on to a sticky label and paste it on your target turrets. When you change loads or decide to hunt in a different elevation such as Death Valley you just make yourself a new label and stick it on the target turrets. In theory it is just as accurate a method as the old 3X56 cards or the cheat sheet on the stock.


    [/ QUOTE ]

    >>written computer programs that will print out custom paste on BDCs.
    If they have something to replace word, I'll send them money today. What do you me written computer programs?
    Nothing new about MS word, excell or printers. Toting a printer to hunting camp with stickly labels is not generally a viable option. What if pressure/temp changes from printout time (night before) and the following evening when you see the nice bull at 1137 yards?

    Nothing really compares to a pocket PC with Exbal, my NF scope with NP-R2 illum reticules and lines every 2 MOA, a quality long range hammer (I have a few from Kirby), lots of practice/experience (I need more of). What I find far absolutely absurd is the pinned Ballistics Programs (Web based & Down-loadable) - Even the pocket PC version is just a table that needs an internet connection to download the data. Who has an internet connection at elk camp?

    I can't see the advantage a BDC has over say my Kirby/Lilja/338 RUM shooting a 300gr MK out the 30" tube, my NF 5.5-22x50mm SCOPE sighted dead on at 550 yards, ExBal , pocketPC, two wind meters, temp gauge, Harris BP, good bino's, patience. I only need dial in a correction c where -2 < c < 2 MOA ; if I use my NF BR, I can get down to 1/8 MOA corrections. Can you do that with 8pt Tahamo? It does sound like a far superior approach to the old fashoned static BCD, but still not the ultimate choice (and you have to pay more for it).

    For an interesting discussion of the old fashioned BCD v. computing with dynamic conditions read BeyondBelief
     
  10. Guest

    Guest Guest

    Bart
    Target turrets are in inches 1/4" or 1/8" per click. where do you get one that is calibrated in MOA,?????
     
  11. Bart B

    Bart B Well-Known Member

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    Old Bear, those 1/4th and 1/8th inch clicks are how much they change impact at 100 yards. They're also how much the change is in MOA. 1 inch at 100 yards equals 1 MOA. They're one in the same.

    At 400 yards, a 1/4th MOA click will change impact 1 inch. The common terminology is to express the click value in minutes of angle.

    Does this help?
     
  12. jwp475

    jwp475 Well-Known Member

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    My ballistics program ( which is the ExBall Nightforce version) will give give drop tables any way that you want them MOA,inches, metric,etc.Acctualy one moa at 100 yards is 1.047 inches most just round of to 1 inch for purposes of conversation.The difference does add up as the range gets longer, 5 to6 hundred yards only amount to a little over 1/4" at 600. but 1000 and beyound the difference of .047 inch begins to show, if one is after precision.
    If you live at say sea level and your bdc is calculated for this alltitude and you book a Deer hunt in another state and the elevation of your hunt is 7500 feet,the difference in correction will be considerable.Let's say that you are shooting a 308 175 grain SMK with a 100 yard sight in, your correction (at 600 yards at sea level and 59 degrees with 78% humidity)is 15 moa or 94 inches the same conditions at 7500 feet elevation is 13.5 moa or 84.7 inces. How do you account for this difference with a bdc? The difference is quite easy to allow for with target knobs, as well as correction for windage. The bdc's are for people that do not totaly understand long range shooting.I started as one of those that did not understand as I had bdc's,but the more you learn the more you will see the weaknesses of the bdc's
     
  13. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    Acctualy one moa at 100 yards is 1.047 inches most just round of to 1 inch for purposes of conversation.

    [/ QUOTE ]More "actually," one minute of angle for shooting purposes has been exactly 1 inch at 100 yards in the USA for over 100 years. It's the trig minute of angle that's 1.047... inch at 100 yards. Kinda like the difference between a statute (land) mile of exactly 5280 feet and a nautical (ocean) mile having about 6080 feet.

    The "shooting" MOA is based on the standard 30 inch iron sight radius on early 1900's target rifles and the target's scoring rings having even inches in diameters. Plus the external scope mount's spacing of 7.2 inches.

    One shooting MOA is equal to exactly 1/3600th of the sight adjustment radius or range. With a 30-inch sight radius, that's equal to .00833-inch movement on the rear sight; exactly 1/3rd of a turn (4 quarter minute clicks) on their 40 threads per inch lead screws. And also equal to .002-inch rear scope mount movement (also 4 quarter minute clicks with the same thread count), or 1/3600th of the 7.2-inch mount radius or base spacing.

    In contrast, European sight adjustments have typically made changes on the target in metric units; 1mm or 2mm at 50 metres or 1cm at 100 metres. They've adopted the USA shooting MOA for some of their rifle scopes.
     
  14. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    The bdc's are for people that do not totaly understand long range shooting.I started as one of those that did not understand as I had bdc's,but the more you learn the more you will see the weaknesses of the bdc's

    [/ QUOTE ]Glad you figured that out.

    For example, there's a 50 inch drop difference with a .308 Win. shooting 190's at 1000 yards going from 600 feet to 6600 feet altitude. That's 5 MOA; enough to miss everything except the body of a brontosaurus using a center hold.