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Test for true BC's

 
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  #1  
Old 12-27-2002, 09:49 AM
 
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Test for true BC\'s

I was wondering if this would work.....

1. Zero Rifle for 100 Yards
2. Shoot for center of 100, 200, 300 & 400 Yard Targets.
3. Measure Muzzle Velocity while doing so.
4. Measure the drops.
5. Put MV and stated BC into ballistic program then keep adjusting BC until the ballistics program matches my actual drops.

Would this be an accurate way to determine true BC?

Also, would my drop charts be accurate past the ranges I shot? (in this case 400 yards)
Or, would the BC change from the bullet slowing down?
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  #2  
Old 12-27-2002, 01:25 PM
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Join Date: Jun 2001
Location: Palmer, Alaska
Posts: 2,539
Re: Test for true BC\'s

John,
It depends on what bullet your shooting and the drag curve it follows more closely, but it will work just like you decribe.

I found one thing I don't like about my handhelds balistic program, it uses only the G1 drag curve and does not give you the option to use any of the others or multible BCs as the Oehler program does. As a result many bullets will start to fly flatter at range than the program predicts when it follows fine out to 400 yards or so.

After you shoot out to 1000-1500 yards or so you should have an idea of what BC is working well through what distance ranges. For accurate charts I use 5 shot groups at each range interval to see a good group center.

In my experience the chart will deviate at longer ranges than actual drop using the G1 curve so the BC on the program will need to be modified to follow actual shot data. Very time consuming task but necessary, with many changing variables like temp, inclination angle etc they should be verified as well to be sure the program predicts drop accuratly with a different input changes. One reason to find a good bullet and stick with IT.
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Brent Moffitt
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  #3  
Old 12-27-2002, 07:28 PM
 
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Re: Test for true BC\'s

What I'm going to do this spring (besides open a 1000 yard indoor range [img]images/icons/grin.gif[/img] )
is to shoot my 338 lapua and my 7mm stw out to 1000 in 100 yd increments. Then I will do what I mentioned with the BC to figure out how the BC changes out to 1000 as well as the first 400.

Sometimes its good to be Obsessive Compulsive [img]images/icons/shocked.gif[/img]
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  #4  
Old 12-27-2002, 10:41 PM
 
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Re: Test for true BC\'s



[ 07-12-2003: Message edited by: S1 ]
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  #5  
Old 12-28-2002, 09:10 PM
 
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Re: Test for true BC\'s

S1, sounds like I should buy the Oehler 43 ballistics Lab instead of just the model 35 chrono.
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  #6  
Old 12-28-2002, 11:42 PM
 
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Re: Test for true BC\'s



[ 07-12-2003: Message edited by: S1 ]
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