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Bullet drop compensation dials (BDC dials)

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  #36  
Unread 05-12-2006, 05:32 PM
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Re: Bullet drop compensation dials (BDC dials)

Jon ,After testing more than 50 Leuopold vx 111 or vari x 111 I haven't found one that moves in True MOA no matter how they're marked on the turret. They always move 15"s when you move them 15 min.Not 15.7". The only scope I've found to move MOA was a Springfield Armory . I was just thinking that a good program could give turret numbers (SMOA)very easily for the guys who have scopes that move in inches.----7mmrhb
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  #37  
Unread 05-12-2006, 07:28 PM
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Re: Bullet drop compensation dials (BDC dials)

I think that all of the confusion is because many scope manufacturers directions explain that their scope move 1/4" per click at 100 yards,but on the turret it reads 1/4 moa.We must understand that 1 moa is 1.0472 inches per one hundred yards(1/4 moa is .2618" not .250" which is 1/4"),so if the scope moves 1" per 4 clicks then the scope adjusts in inches and not minutes of angle.The scope makers and many gunwriters add to this confusion by aserting that 1" = 1 moa.If this is not understood then elevation correction at long range will be of by a cosiderable margin.Pretend that you need 20 minutes of angle of verticale adjustment at 1000 yards and your scope adjustments are in quarters therefore 80 clicks adjustment will adjust for 200 inches of correction at 1000 yards.Now let's say your scope adjusts in minutes of angle the same 80 clicks will allow for a correct of 209.4 inches at 1000 yards.
The programs could easily be made to give correction either way. Also the scope makers could just make the scope adjust in minutes of angle as well
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  #38  
Unread 05-12-2006, 10:56 PM
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Re: Bullet drop compensation dials (BDC dials)

Of course I am saying that measuring is a must, but I was also just simply showing that knowing what your scope is doing is only half the battle. One still needs to know the error associated with the ballistic programs. [img]/ubbthreads/images/graemlins/wink.gif[/img]
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  #39  
Unread 05-12-2006, 11:00 PM
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Re: Bullet drop compensation dials (BDC dials)

Sorry for the confusion on the earlier post. You were saying that there is only one MOA and I now know what you meant. The mathematical version of MOA does not differ from the MOA we are discussing in relationship to shooting. They are one as you said. Great point.


[ QUOTE ]
The programs could easily be made to give correction either way. Also the scope makers could just make the scope adjust in minutes of angle as well




[/ QUOTE ]

Absolutely!! Lets have it. After all, we are paying for it already!
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  #40  
Unread 05-12-2006, 11:46 PM
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Re: Bullet drop compensation dials (BDC dials)

JWP475, I know the MOA click values very well.I believe it was me earlier in the thread that pointed out the difference . I have been converting drop charts with a calculator for scopes that move in inches for many years.I was trying to let others be aware that might not know to check their scopes. Maybe even get someone to change a program.(fat chance)---7mmRHB
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  #41  
Unread 05-13-2006, 05:39 AM
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Re: Bullet drop compensation dials (BDC dials)

[ QUOTE ]
JWP475, I know the MOA click values very well.I believe it was me earlier in the thread that pointed out the difference . I have been converting drop charts with a calculator for scopes that move in inches for many years.I was trying to let others be aware that might not know to check their scopes. Maybe even get someone to change a program.(fat chance)---7mmRHB

[/ QUOTE ]

I was not infering that you did not understand,in fact it was post such as yours,that caused me to try and clear up my point in my earlier post as per response's I realized that I only added to the confusion by not adding enough detail
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  #42  
Unread 05-24-2009, 07:08 PM
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Re: Bullet drop compensation dials (BDC dials)

I read thru this thread and found a lot of agonizing about what is a MOA. This is real simple. A MOA is a "minute of angle" which is 1/60th of a degree. It is a trigonometric term and is already well defined. To eliminate the confusion, one MOA results in 1.0472 inches of deflection at 100 yards. The difference between 1.0472 and 1.0000 inches per 100 yards is no problem at short distances but it will assure a miss if you are shooting at a LaRue sized target at 1000 yards.

Why is there agony? The bench resters measure group sizes by the center to center distance of the two shots fartest apart in a group. Then they subtract the bullet diameter. Since in the early days of bench rest shooting the difference between 1.0000 and 1.0472 inches at 100 yards was negligable so someone called 1 inch at 100 yards a MOA and the rest of the story is agony. See what happens when you try to change scientific definitions. Some not too bright vendors started trying to accomodate hunters by also calling 1.000 inches at 100 yards a MOA. While the attempt to simplify things is a noble thought, it is like the government trying to change the definition of pi.

All this confusion makes the case for the advocates of the metric system. This is another trigonometric term but has the unique advantage of having a tangent value of 1/1000th. The definition of a mil radian is 1/1000th of a radian. There are 2*pi radians in a circle. If you do the math you will find that one mil radian (or just one mil) is 1 meter at 1000 meters or 1 yard (36 inches) at 1000 yards. Now that aint bad but it is a little coarse so some scope manufactures (Scmidt & Bender, NightForce) offer 1/10mil elevation adjustments for their metric scopes (0.36 inches at 100 yards). If you get into the pros and cons of the metric system vs the english system, the metric system wins hands down. There is nothing as sweet as ranging with a mil radian scope reticle.

By the way I recommend calling 1 inch per hundred yards IPHY and 1/10 mil at 100 meters CPHM. At least this clearly defines the four different sets of angular measure being used.

Hope this helps.
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