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Ballistic calculator

 
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  #15  
Old 10-04-2009, 12:49 PM
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Join Date: Jan 2005
Posts: 338
Re: Ballistic calculator

Eric, it is possible that you're using MOA on the ballistic calculator, when your scope is moving in IPHY !! You didn't say what scope you are using but if it's a Leupold it will be moving in inches as do many others. Obviously it would take more clicks to get dialed in and would account for the discrepancy you're seeing.

No need to shoot to test the scope, just put a grid on some cardboard measured in inches with numbers big enough to see at 100 yds, starting with the Zero at the top and numbered down to 33 or so inches. Anchor your gun in a shooting rest ( tape or weight it down ), put the grid at exactly 100 yards and line up your crosshair on the zero. Carefully dial up the scope and see how far it actually moves in one and two revolutions of the turret and see if it returns to zero each time. Make sure you get the paralax adjusted out before you start.

You'll know in a few seconds if your scope is IPHY or true MOA!!

Goodgrouper and I do this on each clients gun before load testing. You would be shocked at the number of clunkers that show up on this simple test !!! ----- RHB
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  #16  
Old 10-04-2009, 12:58 PM
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Join Date: Feb 2009
Posts: 175
Re: Ballistic calculator

The scope is a Leupold LPS. 3.5-14x52.


I'll have to try out the test mentioned. It's raining today, so I am stuck inside.




I am having trouble getting my head around it, because- Do I trust the advertised BC? Or do I trust the chronograph?

The help is greatly appreciated.
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  #17  
Old 10-04-2009, 01:14 PM
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Join Date: Apr 2005
Location: Alaska
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Re: Ballistic calculator

Quote:
Originally Posted by eric2381 View Post

I am having trouble getting my head around it, because- Do I trust the advertised BC? Or do I trust the chronograph?

The help is greatly appreciated.
I've built a dual chronograph setup, and since using it, would never go back and rely on a single chronograph for establishing MVs. I use one Oehler 33 and one PACT, with skyscreens set up on a single rail at 4.5' and 5' skyscreen spacing. This allows me to confirm I'm getting good data. There have been quite a few instances where I have ID'd bad data from one chrono of the other. If the difference in measured velocity is unusually high or low between the two, I know I've thrown a bogus number on one or the other.

With all the time and effort that goes into establishing a reliable drop chart, the last thing I want to do is start the process with bogus MVs.
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  #18  
Old 10-04-2009, 01:31 PM
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Join Date: Feb 2009
Posts: 175
Re: Ballistic calculator

Even though it says Minutes on the dial, Leupolds are really in inches per one hundred yards? How does one go abouts making a drop chart for that?

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  #19  
Old 10-04-2009, 01:49 PM
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Location: Blackfoot, Idaho
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Re: Ballistic calculator

Quote:
Originally Posted by eric2381 View Post
Is it common to find that the advertised BC to not be tue???

I'm discovering that Nosler BT advertised BCs are quite high.

However, different barrels will result in different BCs.
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  #20  
Old 10-04-2009, 01:55 PM
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Join Date: Feb 2009
Posts: 175
Re: Ballistic calculator

It quit raining here for a bit. I'm gonna get away from the wife and kids and go and double check my velocity and check my scope while I'm there.
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  #21  
Old 10-04-2009, 01:58 PM
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Location: Blackfoot, Idaho
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Re: Ballistic calculator

7mmrhb is giving good advice.

I standarized every thing to IPHY for my calculations. It do make a difference.

IPHY is the easiest for me to keep straight in my ol' knoggin.

It is really important that 1 IPHY actually changes 1" @ 100.
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