Ballistic calculator

[eric2381]

[FONT=Verdana, Arial, Helvetica] 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.[/FONT]

[FONT=Verdana, Arial, Helvetica]Below is the calculations that I used originally to get me on target.[/FONT]




[FONT=Verdana, Arial, Helvetica]http://www.biggameinfo.com/index.aspx?page=%2fbalcalc.ascx[/FONT]

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



[FONT=Verdana, Arial, Helvetica].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.[/FONT]


[FONT=Verdana, Arial, Helvetica]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.[/FONT]

[FONT=Verdana, Arial, Helvetica]Thanks, Eric[/FONT]

 

[m249]

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.

 

[eric2381]

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.

 

[NomadPilot]

Drop your BC down a little bit and see if that dope matches better at all ranges.

 

[royinidaho]

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.

 

[eric2381]

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.

 

[eric2381]

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....

 

[royinidaho]

I'm using this thread to sharpen my skills with exbal. Hope you don't mind.

The information provided says that you are zeroed at 272 yds. (2.5" high at 100)

Come ups @ 500 = 5.25

You gave the info for 500. I could find no 750 data Drops)

1.9" LOS above LOB seems a bit high. How was this measured?

You don't need to shoot all of the distances (too time consuming and expensive).

Verify your 2.5" @ 100. Then get good 'actual' drops at say 500, 600 and 750.

These distances should be sufficient to be able to connect the dots.

Post your results and we'll go from there, OK?
Also, is there a local airport where you can get barometric pressure @ altitude, not corrected to sea level?

 

[eric2381]

CANOE -- CNEWS: Weather

I found the current barrometric pressure here.


I measured the sight height with my caliper. I'll measure again, to be sure.


I am bang on 2.5" high at 100 yds. I need to go up 6 MOA to be bang on at 500 yds. I need to go up 1.75 MOA to be right on at 350yds.

 

[eric2381]

I stand corrected. My sight height it 1.7", not 1.9".

 

[eric2381]

That still doesn't bring me around to the numbers that I actually shot.


I'm gonna have to go out shooting again to get some more numbers.

 

[royinidaho]

I stand corrected. My sight height it 1.7", not 1.9".

That'll make a difference!

Formula for determining LOH over LOB.

Distance from top of end bell to bottom of barrel minus ((1/2 of scope end bell diameter) plus (1/2 of barrel diameter at front of scope end bell)) All measured at the same point.

If there is a sloped base then some fudging be necessary.

With the new LOS value and the old atmos data here's what I what I came up with.

As close as I could get thing to jive with your drops are:

100 yds = 2.585" high
350 yds - 1.985 MOA (0.235 MOA or 0.8225")
500 yds - 5.961 MOA (0.039 MOA or 0.195")

Inputs were:
MV = 2965 FPS
Line of Sight above Line of Bore = 1.70"
BC = 0.48

 

[eric2381]

Is it common to find that the advertised BC to not be tue???

 

[liltank]

Is it common to find that the advertised BC to not be tue???

Yes!!! I'm having the same problem that you are having. I am currently trying to find out my range card. I need 13 MOA at 680 and 29.2 at 1070yrds. The problem I am having is getting those to numbers to appear at yardage. If anybody would care to crunch, by all means give it a go. 54deg. 1000ft elev. 60%humidity, 29.94 baro, 2930fps, 200grn SMK.

I've tried adjusting bc. and can get it to match the 680, but not the 1070. It does not give me the proper come up at the longer distance. I wish they had a scratching your head emoticon.

Tank