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Bullet drop compensation dials (BDC dials)

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  #22  
Unread 05-10-2006, 07:54 AM
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Re: Bullet drop compensation dials (BDC dials)

7mmRHB, you've enlightened me. Thanks for pointing out that different folks use different strokes (MOA values, sometimes 1.0472 inch, sometimes 1.0000 inch; for each hundred yards of range). I checked my Sierra manual and sure enough, it lists a MOA equalling 1.0472 inch per hundred yards; never noticed it before.

I've sent e-mail to both Sierra Bullets and Perry-Systems asking about this. I think this has opened a can of something; candy to some, worms to others. I'll share what they say about it. And I'm going to contact all the scope makers and ask them about their MOA standard they use; more info to share. I know what those using external adjustments used; it's the internal adjustment standard I'm interested in.

Old Bear (if you're reading this), I now understand what you were talking about. Coming from his point of view, it makes sense to me. Sorry 'bout not understanding. It would be nice if all the ballistic software folks would list the scope make/model adjustment standards so we could get correct data for sight settings.
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  •   #23  
    Unread 05-10-2006, 11:18 AM
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    Re: Bullet drop compensation dials (BDC dials)

    Bart ,it seems that it would be a simple thing for a ballistics program to give you both options so a guy doesn't have to sit and do math all day to get his charts worked out.

    The reason I discovered this discrepancy in the first place was that sierras first program didn't have a MOA function. I had to figure out the math to get MOA to match the turrets for each scope I was working with. Then when I started looking at the new programs with the MOA function built in I noticed a large discrepancy between the two. A little math solved the riddle but I still have to make my charts the hard way. LETS get this changed !!!!

    Almost all U.S. made scopes are in 1" MOA. How do we go about fixing the problem with the programs.

    Another problem with Sierra Infinity is that when you go to the uphill downhill function they don't have the MOA option available.(bullet path in INCHES only)

    This post is buried where not too many people are reading this or there would be more response. Maybe a new post is in order in Bullets barrels and Ballistics ----7mmRHB
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      #24  
    Unread 05-11-2006, 03:20 AM
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    Re: Bullet drop compensation dials (BDC dials)

    [ QUOTE ]
    7mmRHB, you've enlightened me. Thanks for pointing out that different folks use different strokes (MOA values, sometimes 1.0472 inch, sometimes 1.0000 inch; for each hundred yards of range).

    [/ QUOTE ]
    Yeah, I think it's actually more common for scopes to have MOA adjustments in lieu of SMOA. But this thread should highlight the importance of people actually measuring what their scope is regardless of what is stamped on the turrets. Apparently not many do that. Just a small amount of error can add up after 80, 100+ clicks....

    It's also a reason I like Excel sheets for calculations--so easy to customize. The one I use you can enter whatever your actual click value (that you've measured) is and save yourself a lot of math.
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      #25  
    Unread 05-11-2006, 03:56 AM
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    Re: Bullet drop compensation dials (BDC dials)

    [ QUOTE ]
    If you are printing a label apparrently you are tapeing them to target turrets.

    [/ QUOTE ]
    You are correct. Actually, I'm not sure what an "official" definition of BDC would be. Basically the same in operation as a Kenton, Leupold or the like, except not a $70 laser engraved aluminum piece that you're stuck with forever...or until you buy another one. To me, most of the criticism of BDC's comes from that fact--you'd need a hundred of them for every rifle and nobody is going to buy that many. But sticky labels and tape are cheap and easy to change--just like the drop chart taped to my stock.

    So for that type of BDC, unless you're packing a computer into the field (which I'd guess the majority of people here aren't), there'll be no difference in accuracy. And of course, this is an entirely different thing than somebody who buys, say, an M3 scope with a permanent BDC and asks what velocity he should shoot to make it "on" or somebody who sends the load data to Kenton or Leupold and expects to use the same BDC everywhere forever...quite different.
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      #26  
    Unread 05-11-2006, 05:46 AM
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    Re: Bullet drop compensation dials (BDC dials)

    [ QUOTE ]
    [ QUOTE ]
    If you are printing a label apparrently you are tapeing them to target turrets.

    [/ QUOTE ]
    You are correct. Actually, I'm not sure what an "official" definition of BDC would be. Basically the same in operation as a Kenton, Leupold or the like, except not a $70 laser engraved aluminum piece that you're stuck with forever...or until you buy another one. To me, most of the criticism of BDC's comes from that fact--you'd need a hundred of them for every rifle and nobody is going to buy that many. But sticky labels and tape are cheap and easy to change--just like the drop chart taped to my stock.

    So for that type of BDC, unless you're packing a computer into the field (which I'd guess the majority of people here aren't), there'll be no difference in accuracy. And of course, this is an entirely different thing than somebody who buys, say, an M3 scope with a permanent BDC and asks what velocity he should shoot to make it "on" or somebody who sends the load data to Kenton or Leupold and expects to use the same BDC everywhere forever...quite different.

    [/ QUOTE ]


    This is exactly what I was trying to convey. A label tapped to target turrets has exactly the same precision as a drop chart tapped to your stock.
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      #27  
    Unread 05-11-2006, 03:33 PM
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    Re: Bullet drop compensation dials (BDC dials)

    [ QUOTE ]
    ... this thread should highlight the importance of people actually measuring what their scope is regardless of what is stamped on the turrets. Apparently not many do that. Just a small amount of error can add up after 80, 100+ clicks....

    [/ QUOTE ]Amidst the process of tightening the lid on this can of wiggly worms, I got some feedback from Exbal and Sierra Bullets.

    Exbal e-mailed me a short paragraph explaining that one trig MOA equals 1.0472.... inches at 100 yards. Yes, that's all they said; even when I mentioned that in my e-mail to them. No mention at all of my comments about iron (aperture) sight and the 7.2-inch base separation standard for externally adjusted scopes.

    Sierra Bullets, on the other hand, did better. They reasoned that maybe the two guys behind their ballistics stuff had engineering backgrounds and maybe they made a bit of a mistake using trig MOA (TMOA) instead of the shooting MOA (SMOA) I mentioned. But these two were high-end engineering rocket scientists so they were used to dealing with standard angular units and all the trig functions related to them. But Sierra also made no comments about the base spacing standard for externally adjusted scopes.

    'Twas suggested this thread end and a related one be put on the Bullets, Barrels & Ballistics section, but I think the one for Scopes & Optics would be better. That's the one related to sighting equipment where this thread's info fits into. I'm trying to think of a decent title.... should get one soon....
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      #28  
    Unread 05-11-2006, 04:48 PM
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    Re: Bullet drop compensation dials (BDC dials)

    Bart,It'll be interesting to see the new post and find out how many people were aware of this problem. Maybe we'll find out there are programs out there that offer more options, such as a column for TMOA and SMOA. Michaels program might already do that so I hope he jumps in and gives us his two cents worth. I opened this can of worms ,hoping that more voices might help in getting some changes made. Might just be foolish thinking on my part!!----7mmRHB
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