Computerized Ballistic Solutions

[Blaine Fields]

I'm getting frustrated. I would like some feedback on this idea, but after posting this on another forum got practically zero response. Let me give it a shot here.

There are a couple of companies that have ballistic software on a PDA for use in the field. I bought the Horus product but found various drawbacks and decided to write my own. The problem I had with the Horus was that the firing solution was simply in terms of MOA. What if you wanted a MIL solution? What if you wanted the solution in terms of your particular scope turret?

This is a screen shot of a 1000 yd. solution where wind is at 4 mph from 220 degs and the target is moving at 3 mph at 80 degs relative to the shooter. The solution shows windage in both MOA and MILS, a lead MIL value (which deals with the target's motion) and a "Holdoff" value with combines both windage and target lead.

Note that in the window labled "Turret" is the result "33 - 2". This is the elevation correction of 29.1 MOA in terms of my particular scope turret: turn the turret to "33", then back off two clicks. The reason that this readout is valuable is that on my particular scope, although each click is supposed to equal 0.500 MOA, in fact each click equals 0.451 MOA. So the turret readout converts the elevation correction to my turret scale at a rate of 0.451 clicks per MOA and then tells me what the setting is based upon the scale on my turret knob. This firing solution is based upon the following preset values:

By way of another example, lets say that I put another scope on my rifle and this scope has a BCD that is set up for a .308 Win, 168 gr. bullet. From the setup, you can see that I am shooting something more akin to a 300 WM (actually, a 300 WSM.) Usually, a BDC for the wrong bullet is useless. However, in this screen shot I have had the program output the turret information in terms of the .308 BDC scale.

The program is telling me to set BDC on '900' then back it off three clicks. So, even though I've got the wrong BDC, the program can still use the scale for a different bullet and muzzle velocity.

I'd like any feedback you guys may have concerning this type of output and your thoughts as to how usable this program might be.

Thanks.

[ 10-22-2003: Message edited by: Blaine Fields ]

 

[Brent]

I've got to run right now but it looks interesting, I'll have to read through it when I get back from the range, got to run.

I'm always up for another PDA ballistics program. Does it have different drag models, G5, G7 etc?

 

[Jeff In TX]

The Horror ballistic program, oops I mean Horus ballistic program is just plain awful. End of story!!

They use something called a C1 drag model. I have found no mention of this drag model in any of my ballistic books. I've sent them 3 emails asking them what calculations they are using and how you convert a G1, G5 or G7 BC to their C1. I've never received a response. I did down load their trial ballistic program and gave it a test drive. This has got to be one of the worst written ballistic programs ever. I pulled out my scientific calculator and took the sample bullet profile on their program and used the 100 year-old G1 drag model to see if that was what they were using. Guess what?? My calculations matched the programs exactly. Their advertised state of the art program is based on 100 year-old calculations for a 1 pound one inch round artillery shell. WOW, how accurate do you really think that's going to be!

Think of it this way. According to their ballistic program, all flat nosed, spire point, boat tail, and VLD bullets all have the exact same aerodynamic flight characteristic. There is no way to change drag models with their program. All bullets are treated and calculated the same.

Save your money on this one folks. If you want the best ballistic program written, invest in the RSI Ballistic Lab. The calculations used in this program are the exact same calculations used by the US Army at the Aberdeen Proving grounds.

And do your self a favor and stop using the G1 drag model in your current ballistic programs for your calculations. Use the G1 for Standard Flat based bullets, G5 for standard boat tail bullets, G6 for Spire Point Flat based bullets and G7 for VLD bullets.

Hope it helps

[ 10-22-2003: Message edited by: Jeff In TX ]

 

[Blaine Fields]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> Hope it helps <HR></BLOCKQUOTE>

Actually, it doesn't. I am extremely satisfied with the accuracy of the drag functions I am using. My questions had more to do with whether a real-time program should have windage output in terms of both MOA and Mils and include lead and holdoff values.

My next question had to do with the value of output in terms of the scale on the shooter's scope.

If you have any comment on these issues, I would appreciate reading them.

 

[Nicholas]

I really like the Exbal program!! I took a big 4 point buck with it yesterday at 823 yards.

It will do mil's and MOA and the PC version will let you put any value in for your adjustments.

 

[Brent]

Blaine,

I think Jeff was just trying to emphasize the importance of A PDA program having the correct drag functions for the bullets we use, the G1 is not that. It works OK but, so does using MOA in you mildot scope, you're just always comprimising. To me, the mil data just isn't important, tho I never use mildots and that's why it isn't.

Exbal is the best PDA program on the market in my opinion, but it still offers no other drag curve other than the G1 to keep a guy on target at BOTH 500yds and 1000yds. You give up accuracy at one range to gain it at another because the drag curve doesn't ever match the form of the bullet being used, it's the basis for the form Jeff mentioned.
Take it or leave it, but it's true.

If you want to create a program with mils, I'm sure a bunch of guys would thank you for it and maybe more are even interested in that as a priority, while a sacrifice in the accuracy of the program isn't. For most guys that never really shoot past 6-700yds the G1 may be fine, so you have that on your side.

When Jim at www.shootingsoftware.com makes the program for a PDA it will blow any on the market right out of the water, as I'm sure it will at least have the G5 and G7 curves, and may also have a custom curve based on the form factor from the exact bullet of your choosing like his RSI Shooting Lab program allows you to create from your bullet dimentions.

Right now, IMHO Exbal looks simpler and easier to understand than the windows that you posted here. Exbal is also very flexible and has a customizable BDC analysis and solution in either MOA or MILS that works very well. Good luck with yours too!

 

[Brent]

SR90, congrats on the buck there too!!

 

[Blaine Fields]

Brent, thanks for your thoughts.

With regard to the G1 function: I agree, it doesn't work well with small caliber bullets. However, the scaling factor associated with the G1 function is universal. All bullet makers publish coefficients using the G1 function as the baseline. If you want to use other functions, that's fine, but you will also have to derive appropriate scaling factors as well. So, realistically the approach that makes the most sense (to me at least) is to develop a drag function that uses G1 scaling factors.

For example, here is a graph showing the G1 (Meyevski-Ingalls) function plot for a .30 caliber, 150 gr. flat-based bullet. The drag function above the G1 is based upon a different function (derived by Prof. Arthur Pejsa) but uses G1 ballistic coefficients to scale the function. Note how this function tracks the actual data points extremely well.

[ 10-24-2003: Message edited by: Blaine Fields ]

 

[Jeff In TX]

Blaine,


Didn't mean to come across wrong. Over the last few years I have really gotten into understanding ballistics. One of my biggest pet peeves is all these ballistic programs that use the G1 drag model. Sorry, but they are only accurate out to 350 to 500 yards. If you're really into shooting long distance, beyond 500 yards you might as well do it right and use the right drag model.

I don't care about how they try to massage the G1 drag model. Bottom line any bullet of the same weight but different design ie: spire point flat base, boat tail or VLD is not going to fly the same beyond a given range.

Plugging in the proper drag model can make all the difference in the world. Designing a program with only one drag model is short sighted.

Anyway, sorry if I bent your tail feathers. Have a great weekend.

 

[Blaine Fields]

Jeff,

There is no single drag function that will describe a bullet's velocity from muzzle to zero fps. If you look at the graph above you will see essentially four distinct zones. Supersonic (curvalinear, above 1400 fps); transonic (flat and linear, 1200 to 1400 fps); subsonic (linear, 1200 - 900 fps), and the zero to 900 fps region which is basically flat and linear. Because three of the zones are essentially linear, describing them is not difficult. It is the curvalinear portion at 1400 fps and above that is the problem.

But it turns out that the major practical differences between spire-point, flat based bullets and VLD types has more to do with the rate of deceleration between the two as opposed to the underlying mathematical drag function. So, as Pejsa has shown, it is possible to use a G1 scaling factor together with a uniform drag function as long as the user can also vary the rate of deceleration from bullet type to bullet type. In other words, the shooter must be able to correlate a bullet with a deceleration constant.

I'll tell you what: take your program and input: atm. pressure @ 29.85, temp @ 75, humidity @ 78%, 190 gr. .30 cal. bullet (Berger VLD) with a BC (G1) of 0.583 and muzzle velocity of 2900 fps. My program forcasts an elevation correction of 29.5 MOA for a 1000 yd shot. It is right on in real life. I know because I have shot that bullet under these precise conditions and I am dead-spanking-on.

What does your program forecast using the G1 or G7? If it ain't 29.5 MOA, it ain't right. The Horus program I have (the Atrag2P, ver 2.40) predicts 27.6 MOA. It is not even close to real world.

[ 10-27-2003: Message edited by: Blaine Fields ]

 

[Brent]

Blain,

What is the scope mounting height and altitude you're using, and how have you determined the BC .583 is actually correct out of your gun? According to every other ballistic program out there besides yours, your BC or MV, or both is actually lower than those numbers.

What is the bullet dropping at 400-500-600-700 yards too? Drop at 1000 yards really tells nothing about the curve by itself, and if the scope clicks are not calibrated exactly for MOA the total MOA dialed to zero out there won't be accurate either...

With a 1.5" scope height I have 27.12 MOA with the RSI SL G1 BC using Bergers published .583 BC. Exbal Palm predicts 27.0 MOA, desktop version 27.1 MOA, Atrag1p predicts 27.2 MOA. Oehler BEX predicts 27.1 MOA, LFAD predicts 27.38 MOA...

I wonder why your program predicts such a different number than "all" the others?

 

[Blaine Fields]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> What is the scope mounting height and altitude you're using <HR></BLOCKQUOTE>
Scope height: 2". Altitude: I ignore the altitude because I have the actual field atmospheric pressure. My program will use altitude only as a means to approximate the actual pressure.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> What is the bullet dropping at 400-500-600-700 yards too <HR></BLOCKQUOTE>

The results from my program from 200 yds to 1000 yds are correct. The first time I used the program's output was in a tactical match which involves shooting from 200, 300, 500, 600, 800, 900 and 1000 yds. At the completion of the match (36 total rounds), the total vertical dispersion of the 36 rounds was 10 inches - and at each station I used exactly what the program output. This is very satisfactory performance as far as I am concerned.


<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> I wonder why your program predicts such a different number than "all" the others? <HR></BLOCKQUOTE>
I wouldn't know, except that I don't believe that any of the programs you mentioned use Arthur Pejsa's work. I can say that generally the use of a drag function similar to Meyevski-Ingalls (essentially the G1 model) will yield more optimistic results (as shown on the above graph) than what a shooter will see on the range. There are a number of ways to deal with this, such as calculating differing BCs for different speed regimes. This is how Sierra deals with the problem. Pejsa has dealt with the problem by using a deceleration constant that can be found for each bullet.