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Ballistic program not matching actual

 
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  #8  
Old 10-27-2011, 08:47 AM
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Re: Ballistic program not matching actual

You can figure that the advertised B.C. is correct, but even with a chronograph you can't be sure that your velocity is. Plug in different muzzle veolocities until the ballistics program matches the real drops match. That figure will be your true velocity. Don't necessarily believe your chronograph. If in doubt measure your vejocity at the muzzle and at 100 yards, preferably at the same time. Plug those figures into a B.C. computing program and if the B.C. doesn't match the advertised B.C. then your chronograph is probably off.
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  #9  
Old 10-27-2011, 12:34 PM
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Re: Ballistic program not matching actual

What about some cant in the scope? Is it mounted perfectly?
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  #10  
Old 10-27-2011, 03:20 PM
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Re: Ballistic program not matching actual

Quote:
Originally Posted by twiedenh View Post
What about some cant in the scope? Is it mounted perfectly?
A slight cant to the scope would not effect the high/low much at all. Mostly that will screw up your windage adjustment.
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  #11  
Old 10-27-2011, 03:24 PM
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Re: Ballistic program not matching actual

Quote:
Originally Posted by caryo15 View Post
Lots of data: 308 DPMS, 168 SMK, 2806-2875fps through out the day, 1280', avg. 83 F, avg. BP 30.07, avg. humidity 48.9%

first moa is actual hold - where it impacted, adjustment the computer called for

100: zero
200: 1.75 moa - center, comput: 1.5 moa
300: 4.0 moa - 2" low, comput: 4.0
400: 7.0 moa - center, comput: 6.75
500: 10.0 moa - 3" low, comput: 9.75
600: 14.0 moa - 2.5" low, comput: 13.25
700: 19.0 moa - 3" low, comput: 17.25
800: 25.0 moa - 3" low, comput: 21.75
900: 30.75 moa - center, comput: 27.0
1000: 38.5 moa - 6" high, comput: 32.75

Thanks,
Cary
I used your figures and came up with the following. Average BC of .425, Average velocity of 2850fps.

100-0.0 Moa
200-1.7
300- 4.1
400- 7.0
500-10.3
600-14.1
700-18.5
800- 23.5
900- 29.3
1000- 36.0

These were using average velocity of 2750fps

0.0
1.9
4.5
7.6
11.2
15.4
20.1
25.6
31.9
39.2

That looks pretty darn close to your real impacts.

I used Hornady's ballistic calculator.

Ballistics Calculator - Hornady Manufacturing, Inc
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Last edited by WildRose; 10-27-2011 at 03:42 PM.
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  #12  
Old 10-27-2011, 04:22 PM
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Re: Ballistic program not matching actual

Anyone know the Litz BC for this bullet? I've got it very close but I don't buy the BC.
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  #13  
Old 10-27-2011, 04:50 PM
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Re: Ballistic program not matching actual

Tweaking it a little more I got even closer to what your actual field data shows.

100-0.0
200-1.9
300-4.6
400-7.7
500-11.3
600-15.4
700-20.0
800-25.2
900-31.2
1000-38.0

This was using a BC of .450 and 2,700FPS MV.

Keep in mind that you will virtually never get your field results to be exactly reflective of what the programs spit out as there are simply too many variables that come into play due to the fact humans are involved.

It looks like you are sub .5MOA at almost all ranges to 1000yds and that ain't bad.
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  #14  
Old 10-27-2011, 06:15 PM
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Re: Ballistic program not matching actual

The Sierra matchking has a G7 of .218 and G1 of .427 according to Litz's book.
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