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Ballistic software

 
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  #1  
Old 01-19-2004, 01:53 AM
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Join Date: Jul 2003
Location: Texas
Posts: 147
Ballistic software

I used 4 different ballistic softwares to see how they compared. The set up was muzzle velocity = 3200, BC = .508, bullet weight = 155, sight height = 1.7,zero = 100 yd, temp. = 59, barometric pressure = 29.53, relative humidity = 78.

Results at 1000 yds 30 degree angle

JBM bassistics -246.78 30=-213.9/-30=-209.
Pointblank -247.78 not available
Exbal -246.6 -206.9
Oehler demo -246.56 -211.56

Cosine of 30 degrees = .866
.866 x -246.8 = -213.73
.866 x -247.78 = -214.58
.866 x -246.6 = -213.56
.866 x -246.56 -213.52

I was surprised to see how close all 4 calculated the drop at 1000 yds with a spread of only 1.22 inches compared to a 7 inch spread in results at a 30 degree angle.
I own the Exbal software and the other 3 can be used or downloaded from the web. I would like to see the results from other software that you might be using with a similar setup and comments on accuracy when dealing with angle shooting. For example Exbal only allows you to input 1 number for your degrees when shooting up or down hill and JBM allows you to put in the angle as being up or down. As you can see from the results above this gives you 3 different answers and the JBM method using the up angle comes closest to matching the answer given by multiplying the cosine of the angle by the drop at 1000 yds with 0 angle. Which method is more mathmatically correct ?
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  #2  
Old 01-19-2004, 01:58 AM
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Re: Ballistic software

My results above did not come out very clear. It was supposed to show the results at 1000yds when shooting flat and when shooting at a 30 degree angle, but it all ran together.Also there are 3 numbers for JBM flat, 30 degrees up, and 30 degessr down. I hope this helps.
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  #3  
Old 01-19-2004, 02:48 AM
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Re: Ballistic software

You aren't going to get the correct drop value by simple multiplying the path by the cosine of the shot angle. The formula is:

path = -(drop * cos(a) + scope height) + ((zero drop + scope height)* (range/zero range))

Another point: there shouldn't be an appreciable difference in the path whether the shot angle is positive or negative. It's odd that JBM shows a 5" difference.

[ 01-19-2004: Message edited by: Blaine Fields ]
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  #4  
Old 01-19-2004, 11:51 AM
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Re: Ballistic software

Blaine, in your formula where and how is the zero drop measured ?
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Old 01-19-2004, 11:52 AM
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Re: Ballistic software

Blaine, in your formula where and how is the zero drop measured ?
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  #6  
Old 01-19-2004, 03:42 PM
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Re: Ballistic software

Everything you wanted to know about inclined fire shooting: http://www.exteriorballistics.com/eb.../article1.html

Blaine, I believe the formula should read:

BP = D*cos(a) - SH*{(R - Rz)/Rz} - Dz*R/Rz

Where:

(a) = bore angle to the horizontal
BP = bullet path
D = drop, horizontal range
SH = sight height
R = range
Rz = zero range
Dz = drop at zero range, horizontal

From this formula we can see that the BP correction at any range is: D*(1 - cos (a))
This correction is always substracted to your bullet path.

Maybe a more practical solution to this problem is to use the scope angle of elevation above the horizontal. For example a 175 SMK @ 2680 fps, std. cond., needs to compensate for: 2.5" (drop) + 1.7" (sight height) = 4.2" to zero at 100 yds. This is, 4.0 MOA of elevation are already dialed into the scope when you are zeroed at 100. If your come ups from this 100 yds zero to 1000 yds is 36.6 MOA, you really have 40.6 of elevation into the scope. Think in terms of "scope elevation" instead of drop or comeups!
To correct for any angle at any range multiply "scope elevation"*cos angle
This elegant solution was suggested by BMG Mike back when we had some discussions at SH. It is faster than the solution explained in the Sierra site and produces results with similar accuracy.

For any angle <30, if your base zero is 100 yds you can just use: come ups * cos angle and you'll be veeery close.

Remember all these methods are a simplification of the problem, because they disregard the small variations of bullet drop due to the air pressure and gravity effects on angled shots (which are taken into account in some programs like the Infinity), but these effects are minor and of opposite signs and almost cancel each other out.
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  #7  
Old 01-19-2004, 04:12 PM
JBM JBM is offline
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Posts: 113
Re: Ballistic software

Programs using Siacci methods aren't going to be that accurate since they violate a few assumptions of the flat fire trajectory when shooting at angles like this. My online programs DO integrate the equations of motion and therefore won't have that problem (not will any other software that does the integrals).

For really long range though, you ought to be using something like my MPM (Modified Point Mass) program.
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