Internal Ballistics Software

for the Handloader

While away from reloading proper for the last few years, I've taken time to try to learn more about internal ballistics. This has included playing with software which claims to help you find suitable loads for any cartridge. The prices vary from free to about $150, and as with many things in life, I found you get what you pay for. My observations on these software are presented here. The software I've tried includes the Powley Computer, QuickLOAD, Load From A Disk, CalcuLoader, LoadTech, and CABM and NABM. As a figure of merit, all software was compared to velocities reported in modern load books. Only load books which offered pressure measurements were considered.

The Powley Computer

In about 1960, Homer Powley helped introduce a slide rule which allowed the handloader to predict charges and velocities. Over the years, he improved his equations, and offered more complicated formulas. One set of these formulas was published by William Davis in the NRA's 1981 book on handloading, and these equations in turn have been made into software for PC users. One free implementation is found on this site; it runs in standard browsers, requires no download, and includes a separate page of notes covering its limitations. John Knight in England also offers a free Win32 executable, called WinLoad, which I found works as expected (and there's also a handy calculator for bullet stability as well). There are also versions for Excel and BASIC.

The published Powley equations are intended for the higher pressure rifle cartridges. It attempts to predict conservative charges of IMR powder for strong, modern rifles. It does not attempt to predict charges for low pressure cartridges, nor for reduced loads. It tries to select the powder which for a nearly full case will produce a pressure of about 45,000 CUP, which is about 8000 CUP below what most modern rifles are rated. This slightly reduced pressure provides some margin for error and should also result in excellent barrel life.

In predicting charges, the equations can pick a powder too fast, possibly resulting in pressures too high for comfort. The equations in the older slide rules were even more prone to do so. For a strong modern rifle with good gas handling, you probably won't get hurt using the Powley Computer, but you must learn its limitations by comparing its predictions to the pressure tested loads from loadbooks.

One can learn about the trends in internal ballstics using a Powley Computer. The effects on velocity of barrel length and case capacity are well predicted. The effects of pressure on velocity are not so well predicted. To do so, you must use the Pressure Computer "in reverse," so to speak. The Pressure Computer attempts to correlate chronographed velocity to peak pressure, but only with limited success. The pressure estimates are generally decent, but there are classes of cartridges for which it misses badly.

For the price (free), it's still a useful tool.

Load From A Disk

For home computers, this was one of the first commerical products in this field (perhaps the very first), and W. Square Enterprises is still going after about 10 years, a good record.

The software is derived from Powley's work, with proprietary extensions. Like Powley, it is meant to predict charges for rifle cartridges nearly filled with powder. It does not try to predict the performance of greatly reduced rifle loads or of handgun loads. Unlike the original Powley Computer, it will predict performance with powders other than those from IMR, and it will predict charges and velocity at most pressures. The software also includes dimensions "for 1100 cartridges" and hundreds of commercial bullets.

As compared to load book values, the predictions were generally conservative. I don't recall being given a load that a load book showed would be dangerous. A few hot loads, yes, but the variation was not much greater than can be found among different loadbooks.

I last used this software in about 2001. That version (3.0.3A) could be a bit frustrating to use, with inputs clumsily spread over several somewhat confusing screens, and I ended up throwing my copy away. Many new releases have been made since then, and I have little doubt the software is greatly improved. I can recommend it as an inexpensive alternative to QuickLOAD for those who seek only an estimate of charge and velocity.

QuickLOAD

By far, this is the best software currently available to the handloader. While it's also the most expensive, I think the price not unreasonable, and I recommend it without reservation. It is written in Germany and is offered in the US by NECO. (Also offered is a separate design tool for cartridge cases, QuickDESIGN, which I have not tried.)

QuickLOAD is a simulator, not some fairly simple equation fitted to lab data. It tries to combine a mathematical description of the burning characteristics of each powder with a decent representation of the heat losses to the barrel, etc., and in this way mathematically predict the gas pressure and the velocity of the bullet at every fraction of a millimeter down the barrel.

The software comes with a printed manual which includes a fine introduction to the field of internal ballistics. Included are descriptions of the mathematical representations used for the physical processes which happen inside a gun. To the very great credit of it's authors, the manual spells out all the shortcomings of the program and how these affect its ability to estimate cartridge performance.

Unlike Powley's equations and Load From A Disk, QuickLOAD will predict charges for pistol powders, and it doesn't do too bad a job. The results are not, however, as good as with rifle cartridges.

QL's strong point is correlating rated pressure to velocity. Used as directed, it seems to be able to always get you within 50 fps of what is possible in pressure barrel tests. For pistols, I've seen over 100 fps errors, but it's often better than that.

QL's charge estimations seem to always be low, but that is in the safe direction. (I should note it's charge predictions are really no worse than the other software I've tested.) Related to this is what appears to be a fudge factor on pressure. The manual recommends pressures always be set to 1/8 below that of the cartridge's rating. For instance, if the cartridge is rated at 64 ksi, you should run the calculations at 56 ksi. Done so, the fps predicted is generally quite close to factory ratings. A likely explanation is that cartridges make full pressure (and velocity) only in a tight, factory test barrel. However, some load book data includes pressures and velocities from the pressure barrels, and QL predicts these pressures and velocities go together. An alternate explanation for the 1/8 factor has to do with pressure variations in real loads. Due to normal shot to shot variations, pressures swing surprisingly, and the velocity follows these swings. Cartridge ratings allow some random overpressure, but I suspect the load books are showing velocities at pressures low enough the swings remain within the limits. I really should write the author of QuickLOAD about this, for he has always answered questions promptly.

QL is unique in giving the handloader an insight into internal ballistics. Being a simulator, it will give you plots of pressure, velocity, etc. as the bullet moves down the barrel. You can see the effects on pressure rise rates when changing powders. You can fiddle with powder characteristics to see how this affects powder speed. The bullet engraving input is simplistic, but you will see changes in the pressure curves due to it.

The program allows for rather extreme inputs. I tried simulating a "bomb calorimeter" test by "firing" a low load density charge under a 200 lb 30 caliber bullet. The bullet, of course, doesn't move much, so you can see the pressure rise rates for a closed chamber, and powder burn rates are sometimes measured in this way. By measuring the slope of the pressure cure, I could get numbers not too far from those reported for IMR powders by Davis in the NRA manual.

QL is not a substitute for pressure tested load book data. In the 06/2004 issue of Handloader, John Barsness reports finding QL predictions of pressure for a given charge can be off 10 ksi, when fired in a piezo set up. I find QL does do a superb job of estimating cartridge potential, and it does do a very good job of selecting which class (or "speed") of powders to use to obtain that potential. However, it is not accurate enough to distinguish between two similar powders from different makers, and of course it can't know about all the possible lot variations. It also is clueless about primer effects, which in extreme circumstances can double pressures.

QuickLOAD comes with QuickTARGET, a fine external ballistics program to predict the trajectory of the bullet in flight. I find QuickTARGET flexible and easy to use. QL also will plot a rifle's free recoil, which includes an estimate of the force on scope mounts.

I highly recommend this software. (Please keep in mind the limitations all such software must observe; see below.)

LoadTech

This was AEM Enterprise's successor to their CalcuLoader, which was a relatively inexpensive program I purchased in about 2002. As a testament to their customer support, I received the newly released LoadTech unsolicited, and for no charge, about one year later; my version (1.0) was dated 10/19/03.

CalcuLoader was clearly not a basic Powley derivative, and I don't know how it worked internally. My old notes indicate the rate of change of velocity with charge was quite different than Powley suggested, and the rate of change of pressure with charge was higher and variable, as it is in lab data. It was simple to use but tended to crash. It's charge and velocity estimates weren't too bad. In addition to being very inexpensive, it took little disk space. In its list of case capacities, the values seemed to be always higher than from other sources.

LoadTech superseded it and "is an entirely new product." It was a bit of a disk hog, taking over 110 MB. While they claimed it "renders CalcuLoader obsolete," its velocity predictions were beyond optimistic, at times corresponding to proof load speeds when tasked with predicting loads for low and medium pressure cartridges.

In late 2003, Ed Reynolds of AEM posted comments on the internals of LoadTech on a shooter's forum.

... we have generated a powder model based on the information available from the powder manufacturers, bullet makers, etc. From that we have developed formulas that are "best fit" for a specific powder over the entire range of available data... If the charge or velocity reliability is 98%, then our formulas have come within 98% of the published values provided by ALL of the published data that we have available.

If true, then they have made a statistical fit of published load book data to some simplified model of internal ballistics. I've done some work along those lines myself and have had generally good results.

I don't know what went wrong with that first release of LoadTech, but in 2007 I received word from a recent purchaser of AEM's software that showed the problems I noticed had been fixed. In 2013, I finally decided to update my copy, but sadly, found AEM out of business. I was able to contact Mr. Reynolds, and he kindly gave me a free upgrade to the last copy of their AccuLoad program, of which LoadTech is only one of many useful modules. In limited testing, I find it to produce conservative velocity estimates and reasonable charge predictions for medium pressure cartridges measured in CUP. It was also conservative for high pressure cartridges measured in psi. However, for a larger, high pressure cartridge measured in CUP, it produced charge and fps predictions a bit high, but not dangerously so, especially were one watching fps with a chronograph.

On the whole AccuLoad was a good effort, and I hope Mr. Reynolds will make his work available again.

Fabrique Scientific

On Steve Faber's site, Fabrique Scientific, he offers shareware versions of two different internal ballistics simulators.

One he calls CABM, which is based on an analytic solution attributed to a fellow named Coppock, as found in Corner's standard reference text Theory of the Internal Ballistics of Guns. It is an older, DOS program, and it ran with some hiccups on my PC under WinXP. I recall its predictions were in the ball park.

He also wrote NABM, which appears to have been the most sophisticated simulator offered to the handloader. My PC running XP had trouble rendering the beta release offered for Windows. In an earlier version of his web site, he had some comments on the internals to NABM, but I've lost part of my notes on this and so must recall some details from memory. NABM is a proper simulator, like QuickLOAD, but its representation of internal ballistics is far more detailed. The powder burning is simulated as individual grains of powder, and to a limited extent you can even design your own grain shapes. There are fudge factors to allow one to tweak the model for different lots of powder and the effects of deterrent coatings. (QuickLOAD represents powder burning in bulk, which does account for the effect of deterrent coatings.) NABM also computes an estimate of bullet engraving forces. (QL's bullet engraving is quite crude in comparison.) I suspect primer effects, if addressed at all, were poorly modeled, for these are difficult to quantify.

While its mathematical representation of the internal ballistics parameters was certainly the most comprehensive, I'm not aware Faber had tweaked NABM to the point it outperformed QuickLOAD. Again, NABM is no longer supported, for Faber now recommends one use a strain gauge. Too bad, since mathematical models can give insights the "real world" can mask.

RCBS.LOAD

Sorry, I have not tried this software, but you can read about it at the RCBS site.

Caution

The internal ballistics of small arms are nearly impossible to predict. Small changes in bullet construction will change how readily the bullet enters the bore. The more difficult it is to engrave the bullet, the higher the pressure grows. The greater the pressure gets to be, the faster the powder begins to burn. Pressures can and do rise unexpectedly fast. Another big factor is the primer, for it determines the initial rate of pressure rise, and thus how fast the burning accelerates. Powder lots sometimes vary greatly in burning "speed" as well.

Because the variability of bullet engraving, primer ignition, and powder lots are difficult to quantify, all commercial internal ballistics software simply ignores these effects. (QuickLOAD tries to deal with some of them, but it simply cannot do so with accuracy.) Such software can help you select a powder, but it cannot tell you how much of it to use nor which primer to use. It also can't tell you what fps you can reliably expect to get at a given pressure. For safety's sake, always end load development at a chronographed fps below what the software predicts. Take at least 5% off your expecated fps; your target isn't likely to notice the difference.

The only time you can reasonably expect to reach a certain velocity is if you're using all the same components listed in a load that was tested in a pressure barrel. That means not only the same powder, but also the same primer, the same case, and the same make and model of bullet. Even then, there is no guarentee you'll be getting the same pressure found under test.

10/2013