Range Report Drawing your own Litz type bullet made easy

[Deleted member 10043]

Came across this today looking for an angle formula. I started playing with Litz's data and sure enough it works. It will calculate the BT angle for you.

http://www.border-barrels.com/drag.htm

I got a Speer bullet made for the M1A rifle by American Eagle. I get the nose length by rubbing the bullet across 400 grit sandpaper. It will change the color of the bullet to make that measurement easy.

...

 

[Bearwalk]

Re: Drawing your own Litz type bullet made easy

Nice find.

Loadbase 3 has a very similar analyzer. I look forward to comparing the two, although I think they should be similar as they are using the same code.

 

[jbailey]

Re: Drawing your own Litz type bullet made easy

too bad they don't have an associated manufacturing process attached - i.e. you design the bullet, they manufacture it for you. Good find nonetheless!

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

Litz's data goes back to about 1500 fps and the calculator goes back to Mach .5 so I notice what appears to be the dynamic stability Litz describes comparing his graphs with the calculator's output and graph. The calculator is based on McCoy work, which Litz cites in his book.

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">Came across this today looking for an angle formula. I started playing with Litz's data and sure enough it works. It will calculate the BT angle for you.

http://www.border-barrels.com/drag.htm</div></div>

Nice... There are a few quirks. One - it insists that it knows bullet weight better than the user and refuses to accept corrections: e.g., in its opinion 0.338 Berger Hybrid should be 350gr, and there's no way to convince this nice calculator otherwise. Then when it comes down to ballistic table - it just knows that nobody wants to compute it for further than 1000 yards...

But I was impressed how close it got G7 BC's for this Hybrid bullet, and how it extended them all the way to 0.5 Mach... Good start!

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

Correct. The ballistic table is horrible. I failed to mention that.

I key in the actual bullet weight in the yellow box. It's recalculating it?

Oh okay, I see. Yep, you need to key in the 300 grains yourself on the right side. Otherwise, it will estimate the weight at 350.

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

Actually today it stopped working, giving this:

Software error:

Can't locate GD/Graph.pm in @INC (@INC contains: /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at drag_working.cgi line 45.
BEGIN failed--compilation aborted at drag_working.cgi line 45.

For help, please send mail to the webmaster ([email protected]), giving this error message and the time and date of the error.


Email report to webmaster bounced back.

Do you know how to contact the author, and perhaps get the code?

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

I was getting scriping errors on the ballistic tables at one time as well. Yeah, I wouldn't mind setting this up on a site myself. There are some other contact emails on the contact us link. These guys are Scotland.

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

They sent me an email. It is being upgraded or server is being upgraded something like that. Should be back online soon.

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">They sent me an email. It is being upgraded or server is being upgraded something like that. Should be back online soon.</div></div>
Yeah... Spoke to them - they'd rather not share the code. Which means - if & when I have time, I'll try to find or write the code that can do that. And then perhaps you could set up a Web site to run it.

 

[Bearwalk]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mouse07410</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">They sent me an email. It is being upgraded or server is being upgraded something like that. Should be back online soon.</div></div>
Yeah... Spoke to them - they'd rather not share the code. Which means - if & when I have time, I'll try to find or write the code that can do that. And then perhaps you could set up a Web site to run it. </div></div>

Would try to convert McCoy's code or start from scratch? Let me know if I can be of help. Been meaning to try to tackle this myself, I just haven't found the time...

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bearwalk</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mouse07410</div><div class="ubbcode-body">
Yeah... Spoke to them - they'd rather not share the code. Which means - if & when I have time, I'll try to find or write the code that can do that. And then perhaps you could set up a Web site to run it. </div></div>

Would try to convert McCoy's code or start from scratch? Let me know if I can be of help. Been meaning to try to tackle this myself, I just haven't found the time...</div></div>
I'll start with McCoy code for sure - for if it works, why re-invent the wheel. Perhaps just add some GUI, or maybe CGI interface would suffice. We'll see. Appreciate your offer to help, and will use it.

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

I have plenty of web space to host something if needed.

 

[BryanLitz]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mouse07410</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bearwalk</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mouse07410</div><div class="ubbcode-body">
Yeah... Spoke to them - they'd rather not share the code. Which means - if & when I have time, I'll try to find or write the code that can do that. And then perhaps you could set up a Web site to run it. </div></div>

Would try to convert McCoy's code or start from scratch? Let me know if I can be of help. Been meaning to try to tackle this myself, I just haven't found the time...</div></div>
I'll start with McCoy code for sure - for if it works, why re-invent the wheel. Perhaps just add some GUI, or maybe CGI interface would suffice. We'll see. Appreciate your offer to help, and will use it. </div></div>

Speaking of re-inventing the wheel, why not just use the implementations already available? The McDrag hosted by JBM is solid. I re-coded the McDrag code in Matlab, and not surprisingly, it returned the same outputs as JBM. I find I use the JBM as much as my own code now, depending on if I have Matlab open or Chrome. The tabular output from the JBM code makes it easy to import the data into excel to plot, etc.

The (Basic, I think) code for McDrag and McGyro can be found here:
http://www.jbmballistics.com/ballistics/downloads/downloads.shtml

and here is the .pdf written by the wizard himself (McCoy) who developed the program:
http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA098110

Bear in mind that the accuracy of these prediction codes is 'better than nothing', but not nearly as good as directly measuring drag for a given bullet. You can expect accuracy of +/-10%, better for super/subsonic, worse for transonic.

Here's a copy/paste from the above pdf regarding accuracy (didn't realize you could copy/paste text; possible, but a little sloppy)
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">In Figures 14 through 24, the present t.heory and ex<perimental results are compared for a number of different physical sizes and types
of ordnance projectiles. The agreement is generally quite satisfactory
for a program designed to give quick engineering estinates of drag.
Figure 2S shows the standard deviation (1o) of the MC DRAG program, as
determined by comparison with a large volume of free flight data, plotted against Mach number. The standard deviation is about 6% in CD at
0
subsonic speeds, grows to a maximum of 11% at M 0.95, and levels off
to a 3% error at supersonic speeds. The largest errors at transonic
speeds occur for boattailed projectiles, and this is believed to be
related to the lack of any good similarity parameter for correlating
transonic boattail effects.</div></div>

To put the statements in perspective, +/- 2 standard deviations is the 95% confidence limit. So for supersonic speeds where the SD of error is 3%, you can be 95% sure the program is returning answers that are +/-6% accurate. At Mach .95 where the SD is 11%, you can be 95% sure that the program is returning answers that are +/-22% accurate.

-Bryan

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

When I ran JBM McDrag on your Hybrid 300g bullet, the G7 BC's I got were more different from your experimental data than the BC's produced by Geoffrey's program on Border Barrels Web site. <span style="font-style: italic">Since his site has been down, I couldn't come back and double-check.</span>

Am I correct, interpreting what you're saying as "currently available programs - including McDrag - will not provide CD's & BC's in transonic region with accuracy better than in the ballpark of 10%"?

And back to "why not just use JBM" - I want something that I can run when I'm not on the 'Net. It is less critical for drag coefficients calculators than for ballistic calculators - but still I don't like extra dependencies if I can avoid them.

Tnx!

 

[BryanLitz]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mouse07410</div><div class="ubbcode-body">When I ran JBM McDrag on your Hybrid 300g bullet, the G7 BC's I got were more different from your experimental data than the BC's produced by Geoffrey's program on Border Barrels Web site. <span style="font-style: italic">Since his site has been down, I couldn't come back and double-check.</span></div></div>

I could be mistaken that Geoffrey's program uses McDrag, but I'm sure JBM uses it. There is an input parameter which has to do with the laminar/turbulent boundary layer transition. Sometimes the programmer hard-codes this to what's best for the application, and sometimes it's left to the user to select. If you ran the same program with this parameter set to different values, it would produce different outputs.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Am I correct, interpreting what you're saying as "currently available programs - including McDrag - will not provide CD's & BC's in transonic region with accuracy better than in the ballpark of 10%"?</div></div>

+/- 10% is very good for tranosnic drag predictions, most aeroprediction tools will not do that good <span style="font-style: italic">unless they were trained with specific experimental data sets</span>. The SD of error for the McDrag program is 11% at transonic, which means +/- 22% error at this speed (95% confidence limits, see above).

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">And back to "why not just use JBM" - I want something that I can run when I'm not on the 'Net. It is less critical for drag coefficients calculators than for ballistic calculators - but still I don't like extra dependencies if I can avoid them.

Tnx! </div></div>

Good reason, considering the current lack of access to the Border tool.

-Bryan

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

It appears to be back online. I'll like to refer back to my OP. I like this program because it will estimate the boat tail angle for you and it seems to be accurate. The BC output is not exactly the same as Litz's data but it is close enough for govt work. The only problem I have with Litz's formula once you have all the variables is estimating the RT/R value. Without it I can't use his formuala in the appendix.

Also, the JBM calculator is difficult because it is in calibers and not inches. Example, the nose length has to be >= 1.2 calibers when the entire bullet length is 1.215 ". I don't get it.

 

[Geoff_Kolbe]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">

+/- 10% is very good for tranosnic drag predictions, most aeroprediction tools will not do that good <span style="font-style: italic">unless they were trained with specific experimental data sets</span>. The SD of error for the McDrag program is 11% at transonic, which means +/- 22% error at this speed (95% confidence limits, see above).


-Bryan </div></div>

With great respect Bryan, I think you are pushing a little hard on the errors of the McDrag set of formulae (which the Border Barrels program <span style="text-decoration: underline">does</span> use). McCoy tested his program on a large variety of projectiles from Minuteman missile heads to needles shaped objects and the stated SDs were across the whole range of results from these projectiles. I think we can expect results within the SDs for more conventionally bullet shaped projectiles.

Let us take as an example the G1 standard projectile and see what the Border Barrels program comes up with for Ballistic Coefficients at the spot Mach numbers of 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0. The BCs are 0.97, 0.94, 1.0, 1.0, 0.99 and 1.02

And let us enter the dimensions for the G7 standard projectile, which I think we all agree is quite a different shape as bullets go, and see what BCs the program comes up with. We get 0.99, 1.09, 0.96, 0.97, 1.01, 1.03.

Only one of these results is just outside the stated SD. I think if we are attempting to keep down-range velocities supersonic (or subsonic), as most of us do, then the program gives very usable results. And for long range shooting where the bullet does pass through the relatively inaccurate trans-sonic zone, its passage through this zone is also quite short and so will not contribute much - or even significantly - in the inaccuracy of the ballistics predictions.

I should also add that while programs which are "in the cloud" - such as Border Barrels suite of ballistics programs - may be subject to the minor outages that occur on the Internet from time to time, they are accessible from any platform that has a browser, ranging from super-computers to iphones, regardless of the operating system being used. And, the programs are being run in a double-precision 64 bit environment, with all accuracy benefits implied. Can that be said for an 'app' running on an iphone?

Geoffrey Kolbe

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

Geoffrey,

First - welcome to this great site, on behalf of myself and others!

Regarding your ballistic table and why people may not like it: it's way too crude and limited - and this is before one even looks as the actual numbers it produces.

The following properties are inferior to those in other free online calculators:
<ul style="list-style-type: disc">[*]It generates data in yards only. Not good for me. I want to control the units and have the option of metric. JBM allows me to choose individually per parameters what units I want it in.[*]It steps with 50 yards and stops at 1000 yards. JBM gives me choice of step between 1 and 3000 yards <span style="text-decoration: underline">or</span> meters, and maximum range from 1 to 3000 yards or meters.[/list]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">I think if we are attempting to keep down-range velocities supersonic (or subsonic), as most of us do, then the program gives very usable results.</div></div>
I'd agree in general. Everything works best when you can keep your bullet supersonic all the way to the target.

Unfortunately this approach does not work for ELR where the bullets <span style="text-decoration: underline">have</span> to go through the transonic region.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body"> And for long range shooting where the bullet does pass through the relatively inaccurate trans-sonic zone, its passage through this zone is also quite short and so will not contribute much - or even significantly - in the inaccuracy of the ballistics predictions.</div></div>
This is where I'd like you and Bryan elaborate a little, if possible. By how much will the prediction be affected (increase of the error, in %) by the transonic crossing? If the coefficients are determined not by experiment but by a program like McDrag?

Now, one weird observation. When I use Geoffrey's site to compute G7 BCs for Berger 0.338 Hybrid (300gr) - it gives values very close to what Bryan determined experimentally with one problem: the program insists the <span style="font-weight: bold">bullet weighs 350gr and has density 11.4 gm/cc</span>. And when I explicitly tell the program that bullet's weight is 300gr - it computes bullet density as 9.76gm/cc and gives GC's that are farther away form the experimentally obtained ones than those computed for the incorrect bullet weight of 350gr! Any comments, please? I used laminar nose & turbulent afterbody, except for the last one with all laminar boundary layer.

Program computed 350gr & density 11.4 gm/cc, laminar nose and turbulent afterbody
<table border="1" cellpadding="10" bgcolor="rgb(0,255,0)">
<tr>
<th>Mach</th>
<th>G7 BC</th>
</tr>
<tr><td>0.5</td><td>0.36</td></tr>
<tr><td>1.0</td><td>0.53</td></tr>
<tr><td>1.5</td><td>0.42</td></tr>
<tr><td>2.0</td><td>0.41</td></tr>
<tr><td>2.5</td><td>0.42</td></tr>
<tr><td>3.0</td><td>0.41</td></tr>
</table>


Input weight 300gr, program computed density 9.76 gm/cc, laminar nose and turbulent afterbody
<table border="1" cellpadding="10" bgcolor="rgb(10,230,0)">
<tr>
<th>Mach</th>
<th>G7 BC</th>
</tr>
<tr><td>0.5</td><td>0.36</td></tr>
<tr><td>1.0</td><td>0.49</td></tr>
<tr><td>1.5</td><td>0.38</td></tr>
<tr><td>2.0</td><td>0.38</td></tr>
<tr><td>2.5</td><td>0.38</td></tr>
<tr><td>3.0</td><td>0.37</td></tr>
</table>

Input weight 300gr, program computed density 9.76 gm/cc, laminar boundary layer
<table border="1" cellpadding="10" bgcolor="rgb(0,210,10)">
<tr>
<th>Mach</th>
<th>G7 BC</th>
</tr>
<tr><td>0.5</td><td>0.5</td></tr>
<tr><td>1.0</td><td>0.54</td></tr>
<tr><td>1.5</td><td>0.42</td></tr>
<tr><td>2.0</td><td>0.41</td></tr>
<tr><td>2.5</td><td>0.41</td></tr>
<tr><td>3.0</td><td>0.41</td></tr>
</table>

 

[Geoff_Kolbe]

Re: Drawing your own Litz type bullet made easy

Hello Mouse and thanks for the welcome.

When you say the ballistics table produced by my program is "way too crude and limited" I am not sure which ballistics table you are talking about.

Is it the small table with the G1 and G7 ballistics coefficients and twists for various spot Mach Numbers? Given that Ballistic Coefficients are supposed to be valid across all velocities, I think that giving you the BC at six Mach numbers is an elegant sufficiency. And this table is not the purpose of the program anyway. As for the barrel twist, there is a separate program that gives graphs for twist and stability where you can get as much detail as you like.

Is it the table giving drop in MOA, drop in inches, wind drift, flight time and energy, in 50 yard increments up to 1000 yards? Well - what more information do you want??

You complain that the table only goes up to 1000 yards. True, but there is a "Custom Range" field where you can put in any range you like without limit. Because the bullet is dropping so fast at very long ranges it is often more useful to be able to compute the ballistics at the exact known distance rather than have a table which brackets the known distance.

As for the ranges being in yards only.... well, sorry about that. All the computations are done using "English units" and it is actually not trivial to have the program re-do the calculations in metres. Too, I figured that most English speaking users of the program would want to work (or at least, would be happy to work) in God's units. ;-)

As for your observations about the 338 hybrid, I am not sure what you mean by "the program insists the bullet weighs 350gr and has density 11.4 gm/cc." The program does not "insist" on anything. The default bullet density is 11.4 gm/cc., but you can change the density at any time to whatever you like.

The density of the bullet depends on the bullet construction. If you want to change the dimensions and do a recalculation - as this program allows you to do - then the program assumes that the bullet construction is going to remain the same and so the density will be carried over from the previous calculation.

If you want to change the bullet weight and yet keep all the bullet dimensions the same, then you are effectively wanting to change the bullet construction. Since you are changing bullet construction, you need to change the density to reflect that change in construction, in order to change the weight.

Regarding the results the program gives - all I can say is that I am reasonably satisfied that I have put in McCoy's algorithms correctly and that the program is using them correctly.

I will close by saying that there is a notice in large red letters at the top of the page saying. "READ THE TEXT AT THE BOTTOM OF THE PAGE TO ENSURE YOU GET USEFUL RESULTS". It really would be a good idea to do that.....

Geoffrey Kolbe

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

It took Litz's .308 168 data and entered it into the BB calculator. I then took the average BC between Mach 3.0-1.5, which .215. The Aberdeen proving ground BC for this bullet is also .215. If I remember correctly the APG data was derived from radar.

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">It took Litz's .308 168 data and entered it into the BB calculator. I then took the average BC between Mach 3.0-1.5, which .215. The Aberdeen proving ground BC for this bullet is also .215. If I remember correctly the APG data was derived from radar. </div></div>
I find little interest in averaged BC. The ability to produce <span style="text-decoration: underline">stepped</span> BC, especially extended into subsonic range is what I see as a great benefit and use of such programs and Web sites.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">When you say the ballistics table produced by my program is "way too crude and limited" I am not sure which ballistics table you are talking about.

Is it the small table with the G1 and G7 ballistics coefficients and twists for various spot Mach Numbers? Given that Ballistic Coefficients are supposed to be valid across all velocities, I think that giving you the BC at six Mach numbers is an elegant sufficiency.</div></div>
No it is not that table, but if we're discussing it - yes in the ideal world one BC would be enough for the entire trajectory from supersonic to subsonic during impact. In the real world however few projectiles are exactly G7 (or G1 or whatever Gx) conformant. So for those of us trying to squeeze every possible bit of accuracy out of every piece of equipment, what's "elegantly sufficient" for you is not enough e.g., for me. I prefer to have a parametrized step here as well, and the parametrized boundaries. Some bullets will never fly at Mach 3.0 - so for those I don't need BC at Mach 3.0. On the other hand, in my opinion Mach 0.5 is too coarse a step.

Also, I find just two positions after decimal points insufficient. Please consider making it at least three (shouldn't be too difficult, especially running on 64-bit processor

).

If you're making this program available for me and the likes of me, and would like me to use it - it would make sense to consider addressing my recommendations.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">And this table is not the purpose of the program anyway. As for the barrel twist, there is a separate program that gives graphs for twist and stability where you can get as much detail as you like.</div></div>
You mean - the program provides optimal barrel twist graph based on muzzle velocity? Yes I noticed that, and it's useful. But I change bullets much more frequently than barrels - so I look at stepped BC's much more often.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">Is it the table giving drop in MOA, drop in inches, wind drift, flight time and energy, in 50 yard increments up to 1000 yards?

Well - what more information do you want??
</div></div>
Yes, it's the table that your site calls "Trajectory". As a good start I would consider having for all the data points:
<ul style="list-style-type: disc">[*]Distance (in yards or meters, if you need a formula to convert between the two: 1m = 1.094 yd

).[*]Drop in inches or cm (1in = 2.54cm), and in MOA or MIL - user-configurable.[*]Drift in inches or cm, and in MOA or MIL - user-configurable.[*]Velocity (in fps or m/s, and Mach), Energy, ToF.[*]<span style="font-weight: bold">Ideally - what other don't provide - maximum ordinate when you apply correction at that distance.</span>[/list]
Of course the maximum range and the step must be parametrized. And having Point Blank Range and Mach 1 crossing marked would be useful. And having maximum ordinate for the maximum distance listed or for your "Custom range" would be nice.

Note that other programs - such as JBM - already do <span style="text-decoration: underline">everything</span> I've listed, <span style="text-decoration: underline">except</span> for the maximum ordinate. So ask yourself: why would a person with Internet access go and use your ballistic program that has inconvenient limitations, when on the same Internet for the same price (free) he can go to JBM that would tailor its output in pretty much whatever way he likes?


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">As for your observations about the 338 hybrid, I am not sure what you mean by "the program insists the bullet weighs 350gr and has density 11.4 gm/cc." The program does not "insist" on anything. The default bullet density is 11.4 gm/cc., but you can change the density at any time to whatever you like.</div></div>
I'm bringing your attention to the strange (to me) fact that your program (well, McCoy's program

) generated almost precise G7 BC's (compared to those obtained by direct measurement on the range) - but with the assumption that bullet weight is 50gr more than it actually is. On the other hand, when I provided the actual - and correct - bullet weight, the computed BC's diverged considerably from the empirical result.

I wonder why.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">Regarding the results the program gives - all I can say is that I am reasonably satisfied that I have put in McCoy's algorithms correctly and that the program is using them correctly.</div></div>
I am not accusing either McCoy or your implementation. I'm pointing out at the result that I find strange and hope that somebody could explain it.

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I find little interest in averaged BC. The ability to produce stepped BC, especially extended into subsonic range is what I see as a great benefit and use of such programs and Web sites.</div></div>

Mouse, with all due respect you are not being specific. I'm referring to a specific bullet.

With the SMK 168 you won't see much deviation with high velocity using the higher stepped BC values from the average value. The average BC value is much more useful for longer shots and still can be used for short range high velocity shots. Anyway, the average is calculated from a set of "stepped" BC values without saying. I find it a little ironic that the average from BB stepped calcs just happens to coincide with Aberdeen's radar average. Today I used .215 with the GMM 168 SMK and it is right on the money out to 500 meters using JBM online and the JBM thing on iPod not to mention the bullet itself, which has the final word. Also, the .308 168 isn't any good at subsonic. It's maximum terminal range is out to 800 yards and within supersonic speed.

Also, why isn't two decimal places enough? Why does it have to be to the thousandth? However, if you had to choose between .21 and .22 you would choose .215. But, I don't see it making that much difference in hitting a vital zone size target. It seems to me some people try to use a rifle with the same methodology people use for artillery only with a much smaller shell on the same terrain. It's like the difference between threading a needle and dunking some chick into the water tank, respectively. Example, with the same SMK bullet at 2650 with 100 yard zero we are looking at 800 yards as approx. .21 [-212"]; .215 [-209"]; .22 [-206"]. But using Litz's multiple BC data we are looking at [-209"], which is the same as using the average .215 BC before mentioned. Even using Litz's average BC for the same bullet is [-207"]. As a whole we are looking at an SD of .27 MOA or 2.3". Using Lit'z multiple BC result as a basis of error rate we are looking at approx. .2%. So, I don't see a big problem using two decimal places on a BC for a .308 168 or any like kind bullet for that matter.

As an aside, it is one thing to state an error rate than it is to actually explain it out. The former being like describing dynamic stability on a particular bullet as unstable because it is convenient since dynamic stability has no value and cannot be quantified even though other like kind bullets can be said to not have the same dynamic instability and therefore are stable in the dynamic range, which is the range you state is of the most concern. Put in a sort of parable, E=MC2 is only the short version. In itself it doesn't explain a thing.

 

[Geoff_Kolbe]

Re: Drawing your own Litz type bullet made easy

Hello Mouse

A few quick points.

What are you going to do with a 'stepped BC'? The Border Barrels program gives you complete smoothed drag curve.....

If the stated accuracy of the program is 3%, (using a 64 bit processor with double-precision;-) ) what is the point of giving BCs to 3 decimal places?

You state that the ballistics table is on our 'Trajectory' program. But in the 'Drag' program, once you have derived the drag curve for your bullet shape, if you then press the 'Ballistics' button, you get the ballistics table calculated using the drag curve you just derived. Did you see that?

The trouble with giving the user every choice under the sun is that it clutters up the screen with form fields. And as it is difficult to discriminate between those fields which are important and those that are not, this leads to a confusing layout. Some people like a lot of buttons to push. You are probably one of them. But I - like most people I think - get confused when there are too many buttons to push and too many form fields to fill.

One thing that my programs have been praised for is their clear, clean layout and ease of use. That is because I spent a lot of time trying to separate out the essential information the user really needs to input from the information that just adds informed detail.

Let me ask you. Do you (I mean, you) really need wind drift in centimetres, inches, MILs and MOA? For the civilian shooter (this is not a program for military use) which is going to be the most useful wind drift output?

The program may not have every variant and flavour of output, but in my opinion, the program does the bullet comparison job - which is what you want it for - as well as anything else out there.

But the 'Drag' program is really a bullet designer's tool. Where it really shines is with its visual feedback on the shape of your bullet of interest, the ability to make changes to the shape and see what the changed bullet will look like, and also see what effect the change has on its performance. I believe it is unrivalled in that mode.

Geoffrey Kolbe

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">What are you going to do with a 'stepped BC'? The Border Barrels program gives you complete smoothed drag curve.....</div></div>
I plug those stepped BC's into Ballistic FTE, Bullet Flight and Shooter - to get more accurate prediction in each velocity band of the trajectory.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">If the stated accuracy of the program is 3%, (using a 64 bit processor with double-precision;-) ) what is the point of giving BCs to 3 decimal places?</div></div>
For the fun of it, perhaps...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">You state that the ballistics table is on our 'Trajectory' program. But in the 'Drag' program, once you have derived the drag curve for your bullet shape, if you then press the 'Ballistics' button, you get the ballistics table calculated using the drag curve you just derived. Did you see that?</div></div>
I confess - didn't look. Regardless, usually I play a lot with the calculations - so that one table with 50 yard step and 1000 yard range won't be useful for me anyway.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">The trouble with giving the user every choice under the sun is that it clutters up the screen with form fields. And as it is difficult to discriminate between those fields which are important and those that are not, this leads to a confusing layout. Some people like a lot of buttons to push. You are probably one of them. But I - like most people I think - get confused when there are too many buttons to push and too many form fields to fill.

One thing that my programs have been praised for is their clear, clean layout and ease of use. That is because I spent a lot of time trying to separate out the essential information the user really needs to input from the information that just adds informed detail.</div></div>
I see. Yes this is a very good point. If you <span style="text-decoration: underline">already have</span> a user base for this particular level of details and complexity - then please disregard my comments and keep doing what you've been doing before. Because there already are programs that satisfy my needs.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">Let me ask you. Do you (I mean, you) really need wind drift in centimetres, inches, MILs and MOA?</div></div>
Yes, I need MILs (for both drop and drift). Either inches or cm would do, and inches are better on this side of the Puddle.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">For the civilian shooter (this is not a program for military use) which is going to be the most useful wind drift output?</div></div>
I'll let the civilian shooter speak for himself.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Geoff_Kolbe</div><div class="ubbcode-body">The program may not have every variant and flavour of output, but in my opinion, <span style="font-weight: bold">the program does the bullet comparison job - which is what you want it for - as well as anything else out there.</span>

...the 'Drag' program is really a bullet designer's tool. Where it really shines is with its visual feedback on the shape of your bullet of interest, the ability to make changes to the shape and see what the changed bullet will look like, and also see what effect the change has on its performance. I believe it is unrivaled in that mode.</div></div>
I see. Yes, a very good point. Yes this is a usage mode that I did not think about. It can be very useful.

Thank you for explaining!


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">Mouse, with all due respect you are not being specific. I'm referring to a specific bullet.</div></div>
With all due respect I don't see how/why it matters. I'm speaking of my principal preference for using stepped BC's because they allow to fine-tune the trajectory and account for imperfect match of the projectile to G7 standard. You're saying that the average BC matches the average of stepped ones. Yeah, so...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">With the SMK 168 you won't see much deviation with high velocity using the higher stepped BC values from the average value. </div></div>
So...? I happen to not use SMK 168gr at all, in case it matters...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">The average BC value is much more useful for longer shots and still can be used for short range high velocity shots.</div></div>
I think it's the other way around. Stepped BC's are much more useful for longer - and short range - shots because they accommodate for the "mismatches" between G7 and the specific projectile.

Average BC is a way to make do with what you have, so it's somewhat inaccurate here and there - but on the average should allow to hit a man-sized target.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">Anyway, the average is calculated from a set of "stepped" BC values without saying. I find it a little ironic that the average from BB stepped calcs just happens to coincide with Aberdeen's radar average.</div></div>
Yes it's nice, and it's good to observe. I wonder if one can conjecture from this that McDrag at least in some cases gives results much better than 3% accuracy. Or perhaps the conclusion should be the opposite: those stepped BC's are not accurate enough by themselves - and only when averaged together, the errors compensate each other and one gets the accurate - albeit single BC.

<span style="font-style: italic">One patient is dead, another is running high fever. The average patient temperature in the hospital is normal.</span>

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

Mouse, you are looking at the forest and not seeing the trees. In my example, Litz's output is the same as Aberdeen's radar data output, which is the same as the BB output. Your biggest concerns are in areas that can't be quantified such as dynamic stability and the yet determined imperfection of the G7 standard. Nevertheless, others with much more knowledge and experience than us have gone to great lengths to get close enough so we can use this data in the field with accuracy. So, I'm still confused on what is the point you are trying to convey.

 

[mouse07410]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">Mouse, you are looking at the forest and not seeing the trees.</div></div>
So enlighten me - what is it that I'm not seeing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">So, I'm still confused on what is the point you are trying to convey.</div></div>
I can see that.

In short: stepped BC allow for greater accuracy, which is why every decent program today supports it.

What I don't understand is what's your point. Is it that averaged BC should be - and is - good enough? And the reason is that when you average from radar data and from BB prediction you get the same average value? At least for one bullet?

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

You're deflecting again, which is a defense mechanism. I'm still confused on why you are so down on data output that has nothing to do with the areas of your concern, which have no value. In other words, its magic and nobody can explain it and that is a fact. Seems you picked this hill to die on and it is better for me to just go around it. You win. I'm not in the mood for a ego pissing contest because they just go on and on. When you find that magic bullet, and I'm sure you will, let us know. Peace. Out.

 

[Geoff_Kolbe]

Re: Drawing your own Litz type bullet made easy

Well, I would like to say thank you to everyone - including Mouse - for their comments. I hope everyone goes on using the program and has fun with it, despite restricted output formats which means you can't have tables out to 3000 metres, wind drift in MILS and terminal energies in Joules

I may give the option for distances in metres. I very nearly did, but persuaded myself that the English speaking users of an English language program would probably get by with yards if not actually prefer yards.

As for MILS, in his book "A Rifleman Went to War" Herbert McBride described MILS as a useless abomination and how artillery and "emmagee" shooters make great efforts to find a way to use minutes instead of MILS on their pieces. That was almost a hundred years ago now, but time has not made them any more useful or natural as far as I am concerned. So, you won't be getting MILS.

Thanks again,

Geoffrey Kolbe

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

No problem!

 

[Deleted member 10043]

Re: Drawing your own Litz type bullet made easy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">

Also, the JBM calculator is difficult because it is in calibers and not inches. Example, the nose length has to be >= 1.2 calibers when the entire bullet length is 1.215 ". I don't get it. </div></div>

Sorry to quote myself but I read McCoy's papers (thank you, Bryan) and the caliber length is based on a reference size. You can't use the JBM calculator without knowing the reference size. If a bullet is .308 caliber then .3091 equals 1.0 caliber for measuring length and diameter in calibers. If the bullet length is 1.215" than its equivalent length in caliber is 3.931. Also, the JBM calculator will output the much needed RT/R variable for Litz's G7 formula on page 573.

As an added bonus the output calculates up to 25 stepped BC values. I know somebody that would like that.

http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi

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