I added another feature to Modern Ballistics for the Field. It now gives you the approximate maximum range for your bullet under the given environmental conditions.
The View From North Central Idaho
Ramblings on explosives, guns, politics, and sex by a redneck Idaho farm boy who became a software engineer living near Seattle.
Bug Report:
(Using a Blackberry Curve)
Initial page shows results for Cartridge: 30-06, Firearm: Win 70 30-06.
Change drop-downs to Cartridge: 338 Lapua Magnum, Firearm: AR-30. Click Update.
New page shows results for Cartridge: 30-06, Firearm: Win 70 30-06.
Again change drop-downs to Cartridge: 338 Lapua Magnum, Firearm: AR-30. Click Update.
New page shows results for Cartridge: 338 Lapua Magnum, Firearm: Win 70 30-06.
Again change drop-down to Firearm: AR-30. Click Update.
New page shows results for Cartridge: 338 Lapua Magnum, Firearm: AR-30.
That is very odd. Can you duplicate the problem with a desktop browser or only on the Blackberry?
Ahhhh! I see what is going on. Anytime you try to change more than one item it messes up. I can duplicate the problem.
Thanks!
I found the problem.
It is a bug in the way ASP.NET handles cookies. It’s a known issue that they can’t fix without breaking a lot of code belonging to other people. I’ll have to rearchitect some of my code to get around it.
Thanks for noticing it. I’ll try and get that fixed this weekend.
The United States Gun Owners Association is UP and running, you and your readers are invited!! We need ALL the help we can get!
The bug is fixed. There was a bug in the “Delete All Data” link that I found and fixed as well.
What exactly are the dynamics used to compute the ballistics? Based on supersonic aerodynamics I presume? Does the program actually solve the continuous-time differential equations? If so, does it use simple-differencing with a small time-step, or does it use RK or something else more sophisticated?
It’s based on Modern Practical Ballistics by Arthur J. Pejsa. Awesome book–at least for a geek like me. It gives closed form answers to questions of drop, time of flight, and target velocity. From these numbers everything else is simple trig.
The equations are so simple one can do it by hand on a simple scientific calculator (or a slide rule if you were really hard core). I was a bit skeptical and did a lot of tests. The clincher was when I mounted a scope on my rifle and zeroed it at 200 yards. Then I went to a different range a few weeks later with completely different weather conditions and put my first three shots into the X-ring at 1000 yards.
It gives closed form answers to questions of drop, time of flight, and target velocity.
Really? There must be some simplification. I’d like to compare the closed form solutions with what you get if you run unsimplified dynamics through a iterative solver.
The clincher was when I mounted a scope on my rifle and zeroed it at 200 yards. Then I went to a different range a few weeks later with completely different weather conditions and put my first three shots into the X-ring at 1000 yards.
That’d do it, but I’d still like to compare the error in computation with a more accurate system.
http://en.wikipedia.org/wiki/External_ballistics
That’s a neat page on the subject.
Pejsa claims the solution presented is exact. He is not some amateur. Exterior ballistics is his profession.
If you have “a more accurate system” available to you I would be glad to contribute to the effort to compare the two. But every single test I have done with real bullets in real guns at various altitudes and temperature concluded that his solution was, within my error of measurement, exact.
The simplification is that there are four different velocity zones;
1) 1400 fps <= V 2) 1200 fps <= V < 1400 fps 3) 900 fps <= V < 1200 fps 4) V < 900 fps For each of those velocity ranges there is a simple expression that describes the drop, velocity loss, and time taken by bullet to traverse the given distance.
Note: the following is a minor quibble and not meant for serious argumentation:
Exact is a strange claim when he uses assumptions and simplifications. Also, that wiki page notes that:
So you need to know your bullet, otherwise there’s a bit of a guess at the value of the extra slope constant factor. Seems that a few test shots with the bullet in question is enough to get close to the correct value.
If you have “a more accurate system” available to you I would be glad to contribute to the effort to compare the two.
The wiki page noted earlier does describe full 6DOF models but does not get into detail except to say that detailed knowledge of drag etc. are required for them to work properly. That’s what I’d like to have a go at, I need the drag models first, then the dynamics shouldn’t be too bad.
This looks like the real-deal here. Seems that for you and me (and most everyone else) that your experience dictates that the Pejsa model is just fine though.
My issue with another simulator is that how do we know it models reality any better than the Pejsa or Mayevski models? If you have Doppler data then I’m game. That is real world data not another model.
I guess, but the goal is to predict bullet trajectory for any situation without having to test in the field. Acquiring Doppler data for every bullet type would be prohibitive. On the other hand, if one had access to a nice CFD tool, that’d probably do it. IIRC, CFD tools are pretty good for supersonic flow.
Acquiring Doppler data for a few bullet (or even one) types and comparing to Pejsa’s predictions would answer the important questions. And supersonic models don’t get into the difficult area (and to be honest, I haven’t tested Pejsa’s model below supersonic except with .22LR).
True, the Doppler data would allow you to verify your model, or help with formulating a new one. You’d need the Doppler data to validate your CFD stuff too.