New BBT "P-Max" internal ballistics program

[borbal]

Many of you many have used my online external ballistics software at http://www.geoffrey-kolbe.com/external_ballistics.htm

The eventual goal was, '...a collection of ballistics programs will enable the estimation of all the ballistic information needed from "click" to "thump"...' and I have been putting the last brick in place with an internal ballistics simulator.

It is similar to QuickLOAD, which has been around for over 20 years, and the new GRT software which saw the light of day last year, in that it is a numerical simulation using closed bomb data to generate models of powder energy and burning rates. The virtual charge of powder is then 'ignited' and progress of what happens next is determined by the physics. It is purely a numerical simulation and there are no assumptions about peak pressures or muzzle velocities. Unlike these two programs, The BBT "P-Max" simulator can be accessed online using any device with a browser. It does not have to be downloaded onto a device with an operating system for which the program was written.

One thing the P-Max simulator does have in common with QuickLOAD and GRT is that it needs a large library of powder types to be really useful. But that is not easy as powder companies are very reluctant to part with their powder data - particularly US powder companies. The reason is that they do not want to fall foul of the anti-terrorist legislation and so will not release information which might be potentially useful to enemies of the United States. Well, it is early days and so far, I only have the data for the Chemie Swiss "RS" range of powders and a couple of Vihtavouri powders. But it is a start.

Anyhow, you can access the simulator at http://www.bbt.scot/ballistics/pressure.htm

I would be interested to know what you think about it. Is it easy and intuitive to use? Does it give results which are reasonable compared to your experience? One thing you should watch out for is that the case capacities required are the case capacities behind the loaded bullet, NOT the case capacities to the mouth of the case.

Thanks

Geoffrey Kolbe

[Gandy]

Works on this link many thanks. 

[banus02]

good evening,i am a little concerned about the pressure readings,they seem a bit high, my theoretical load data is n165 powder at 46.5 grs 95gr nosler ballistic tip,usable case capacity of 51 h20 federal 243 case, over all length will be  2680". i need to make a muzzle energy of 1700 ft lbs to be deer legal.also the 46.5 gr powder weight is a lot higher than the vit load data.

[borbal]

On 7/30/2020 at 8:37 PM, banus02 said:

good evening,i am a little concerned about the pressure readings,they seem a bit high, my theoretical load data is n165 powder at 46.5 grs 95gr nosler ballistic tip,usable case capacity of 51 h20 federal 243 case, over all length will be  2680". i need to make a muzzle energy of 1700 ft lbs to be deer legal.also the 46.5 gr powder weight is a lot higher than the vit load data.

Sorry for the late reply, just saw your message

You don't give a barrel length, but let us assume it is 23 inches, which is the barrel length in the online Vihtavuori reloading charts for the 243 Win cartridge. There we see that with 46 grains of N165 behind a 95 grain Berger "Classic Hunter", the muzzle velocity is 2918 ft/sec. The P-Max simulator predicts 2952 ft/sec, which is pretty fair agreement. P-Max predicts a pressure of 3350 bar, which is a very reasonable pressure... and the muzzle energy is 1839 ft-lbs, which is comfortably higher than your 1700 ft-lbs requirement.

You say you are "concerned about the pressure readings"..... Is that the signs of pressure in your rifle or the pressures that P-Max predicts?

Geoffrey Kolbe

[banus02]

good evening geoffrey,thank you for your reply. my rifle is a tikka t3 with a 20" barrel 1 in 10 twist.the vit pressure does not agree with the p-max pressure and the one load i have tried was a bit fierce and my chrono failed to register the speed,my load was 45.6gr of n165 95gr nosler b/t seated to nosler book seating depth,<2680>,hope this helps. ian,<i use psi measurements not bar>

[Popsbengo]

Hi Geoffrey

My real-world results are very similar to your app prediction and I have some data to share:

32" 1:10 barrel

.338 Lap Mag,   Hornady 285gr ELD-M seated longish to 10 thou jump.   No HbN or moly treatment etc

Lapua case trimmed to 2.908" overall length;  usable case capacity measured with bullet seated -   101.70 gr H2O

Viht N570 - 93.5gr,    CCI Mag Primer

Predicted velocity  2854 fps.  vs.  measured velocity   2880 fps (at 20C 70%Rh  985 mb absolute).

Interestingly QL predicted 2797 fps with 98.8% powder burnt where your app predicts 92%,  anecdotally there was evidence of unburnt powder so more in keeping with your prediction (?).

[Popsbengo]

Hi Geoffrey, I have some more real-world data for you

6.5CM. 30" 1:8 5R.     Berger 144gr Hybrid set at 2.901 COAL nominal

Lapua Cases small primer,  trimmed to 1.909,  usable case capacity  46.3gr H2O

44gr RS62,   CCI BR4 primer. powder temp 20degC (measured)

Pretty average day;  20C, 65%, 1015bar abs.

Your MV calculation  2850 fps;   actual  2880fps (high of 2887,  low of 2877)

other load increments from 43gr to 44.5gr were very similar to predicted

Pretty damn good I'd say.