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Ballistic calculator

 
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  #1  
Old 10-03-2009, 08:25 PM
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Ballistic calculator

Hello, I am having a bit of trouble, and can't quite get it to work for me. I have the load that shoots great in my rifle, and it groups well all the way to 750yds. I want to make a come up card for it. I used the ballistic calculator below to figure things out, but when I tested it in real life, it was slightly off. Close, but not perfect. How do I make the adjustment on the ballistic calculator to tell me the drops for all the ranges? My true drop at 500 yds is 24 clicks or 6 MOA. Not the 5.5 MOA the calculator says.

Below is the calculations that I used originally to get me on target.




http://www.biggameinfo.com/index.aspx?page=%2fbalcalc.ascx

Muzzle -1.9 Infinity 3050 3718 78.43 0.000 0.0 NaN 1379
25 -0.4 7 3004 3607 77.25 0.025 0.0 1 1318
50 0.8 -6 2959 3499 76.08 0.050 0.1 1 1259
75 1.8 -9 2914 3393 74.93 0.076 0.3 2 1202
100 2.5 -10 2869 3290 73.78 0.101 0.5 2 1148
125 3.0 -9 2825 3190 72.65 0.128 0.9 3 1096
150 3.2 -8 2782 3093 71.53 0.155 1.2 3 1046
175 3.1 -7 2739 2997 70.42 0.182 1.7 4 998
200 2.7 -5 2696 2905 69.32 0.209 2.2 4 952
225 2.0 -3 2654 2814 68.24 0.237 2.8 5 908
250 1.0 -2 2612 2726 67.16 0.266 3.5 5 866
275 -0.3 0 2570 2641 66.10 0.295 4.3 6 825
300 -1.9 2 2529 2557 65.04 0.324 5.1 7 786
325 -3.9 5 2489 2476 64.00 0.354 6.1 7 749
350 -6.2 7 2449 2396 62.96 0.385 7.1 8 714
375 -8.9 9 2409 2319 61.94 0.415 8.2 8 679
400 -12.0 11 2369 2244 60.93 0.447 9.4 9 647
425 -15.4 14 2331 2171 59.93 0.479 10.7 10 615
450 -19.3 16 2292 2099 58.94 0.511 12.1 10 585
475 -23.5 19 2254 2030 57.96 0.544 13.6 11 556
500 -28.2 22 2216 1963 56.98 0.578 15.1 12 529
525 -33.4 24 2178 1897 56.02 0.612 16.8 12 502
550 -39.0 27 2141 1832 55.06 0.647 18.6 13 477
575 -45.0 30 2104 1770 54.11 0.682 20.5 14 453
600 -51.6 33 2068 1709 53.17 0.718 22.5 14 430
625 -58.6 36 2031 1649 52.24 0.755 24.6 15 407
650 -66.2 39 1996 1591 51.31 0.792 26.8 16 386
675 -74.4 42 1960 1535 50.40 0.830 29.2 17 366
700 -83.1 45 1925 1481 49.50 0.868 31.7 17 347
725 -92.4 49 1890 1428 48.61 0.908 34.3 18 328
750 -102.3 52 1856 1377 47.73 0.948 37.0 19 311
775 -112.8 56 1822 1327 46.86 0.989 39.8 20 294
800 -124.0 59 1789 1279 46.00 1.030 42.8 20 278



.308 cal Nosler BT. BC of 0.507. 3050fps. Sight height of 1.9" Elevation of 2365ft. Temp of 60 degrees F. Zero range is 270yds.


Can somebody else figure this out? Any questions about my question, please ask so I can make a range card to dial in elevation drops.

Thanks, Eric

Last edited by eric2381; 10-03-2009 at 10:25 PM.
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  #2  
Old 10-03-2009, 09:55 PM
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Location: Superior, WI
Posts: 65
Re: Ballistic calculator

Eric, I ran your numbers but used 2900fps and it gave me 6 M.O.A at 500 yards try this and look at the other numbers to see if they match your acual drop at the range.

Hope this helps.
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  #3  
Old 10-03-2009, 10:25 PM
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Join Date: Feb 2009
Posts: 175
Re: Ballistic calculator

Thanks for replying. That's why I'm confused. I am exactly 2.5" high at 100 yds. And I need to go up 6 MOA to be bang on at 500 yds. If I lower the velocity to 2900 fps on the calculator, it puts me at 2.9" high at 100 yds, but I would be adjusting 6 moa up for 500 yds. This doesn't work, since I am keeping my 2.5" high at 100 yds zero.


I'm sure it's something simple, I don't know why I can't get my head around it.


I am 2.5" high at 100 yds.
average velocity for 5 rounds is 3050fps
elevation of 2365 feet above sea level
centre of scope is 1.9" above the centre of the bore
180gr Nosler BT, advertised BC of 0.507
temp. of 60 degrees F


I don't care if my zero is actually 270 yds, that is just what it worked out to be when I made my first range card. I do know that I want to stay at my 2.5" high at 100 yds.

Thanks again.
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  #4  
Old 10-03-2009, 10:26 PM
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Join Date: Aug 2009
Location: Cheyenne
Posts: 512
Re: Ballistic calculator

Drop your BC down a little bit and see if that dope matches better at all ranges.
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  #5  
Old 10-03-2009, 10:36 PM
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Join Date: Jan 2004
Location: Blackfoot, Idaho
Posts: 7,994
Re: Ballistic calculator

I have spend the last two days walking back and forth to the 1K target doing the same thing as you.

All loads chono'd. Wind and mirage was a bear on day one but I got close. I had to reduce the BC from 0.496 tp 0.43 to get the drop chart work at 1K. Today I got three shots in a no wind condition and validated the 0.43 bc. What a downer that is.

The interesting thing is that the 500 and 800 come ups remained the same with the reduction in BC. Will validate this though.
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  #6  
Old 10-03-2009, 10:36 PM
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Join Date: Feb 2009
Posts: 175
Re: Ballistic calculator

I dropped the BC all the way down to .440 and it matched for my real shooting at 500 yds. But, it is quite a ways off for 750yds.
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  #7  
Old 10-03-2009, 10:39 PM
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Join Date: Feb 2009
Posts: 175
Re: Ballistic calculator

I've been shooting quite a bit. Am I gonna need to shoot all the distances and make up my own drop chart?

I thought that I could shoot a few of the ranges, then sort of connect the dots....
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