Muzzle Energy for Palm

Energy.PRC (5K) is a HotPaw Basic application for the Palm organizer that you can use to calculate muzzle energy, efficacy, and sectional density for firearm cartridges. You enter the bullet weight in grains, its velocity in feet per second, and its diameter in inches, and the application computes energy in foot pounds, efficacy, and sectional density in pounds per square inch.

This palm application is a subset of my Muzzle Energy Computer web page, allowing you to carry these computations in your pocket.

My thanks to L. Neil Smith for requesting this application, providing me the motivation to write it.

If you like it, please send whatever you think it's worth (suggested price: $5). Either wire to via PayPal, or send me email requesting a snail mail address for your cash, check, or money order.


If you already have HotPaw Basic (AKA yBasic), you can simply install Energy.PRC on your Palm, and click on the resulting "Energy" icon. Otherwise, go to the HotPaw page and download the Basic interpreter and MathLib. Or you can download my local copy of (110K), which contains the two needed PRC files. You'll want the real distribution if you intend to do any programming. If you just want to use the energy calculator, you can get away with just the PRCs.

The source for Energy.PRC is in Energy.txt (3K). You can paste this into your Palm's memo pad via Palm Desktop, and customize it. To save a new icon including your modifications, you'll need to grok the yBasic documentation. (119K) contains this entire directory, for off-line browsing.


Enter numbers on the dotted lines to the right of the "Weight", "Velocity", and "Diameter" labels, using Graffiti or the keypad. Press the "OK" button to compute "Energy", "Efficacy", and "Sec. Dens.".

To save a weight/velocity/diameter setting, enter a "Name" for it (don't use a colon character, ":", in the name or you will likely become confused), and press the "Calc2" button.

To restore a previously saved setting, enter its "Name", and press the "Calc" button.

Saved settings are stored in the memo pad in a memo named "#Energy". You can edit that memo "by hand" if you wish, either on your Palm or in the Palm Desktop application on your PC. Each line is of the form:

The other buttons work as follows:
0-9, "-", "." self-inserting
"clr" Clears the field containing the cursor
"<-" Erases the character before the cursor
"En" (Enter) Moves the cursor to the next input field
"Done" Exits to the application launcher
Paste the contents of energy-seed.txt into a new memo to seed your muzzle energy calculator with the following Remington loads:
223.223 Remington (5.56 Nato), the M-16/AR-15 round
ak7.62x39, the AK-47 round
308.308 Winchester (7.62 Nato), the M14/M1A/FAL round
30-06.30-06 Springfield, the M1 round
444.444 Marlin, my favorite big bore lever gun
9mm9mm Luger, the army issue mouse gun round
357.357 magnum, a stiff round for a small revolver
40.40 S&W, the new man-stopper
45.45 ACP, the old original & effective 1911 man-stopper
44.44 Magnum: "Do you feel lucky, punk?"
slugShotgun slug

Energy is as defined in physics: 1/2 mass times velocity squared. Mass in the English measurement system is measured in slugs. A slug weighs slightly more than 32 pounds under standard earth gravity. There are 6999 grains in a pound. Velocity is measured in feet per second, exactly as you enter it. The English unit of energy is foot pounds.

Efficacy is a measure proposed by L. Neil Smith. It is defined as energy in foot pounds multiplied by projectile cross-sectional area in square inches. Neil says that this is a pretty good indicator of the relative efficacy against live targets of different projectiles and loads. In an email about the Muzzle Energy Computer page, Neil wrote, "I'm not absolutely certain of its applicability to rifles (although it looks pretty good and is fine for slugs and rifles like .45/70). There are other factors at work above 2000-2500 feet per second. But every year that passes convinces me more that this is the perfect program for predicting handgun performance."

Sectional Density ("Sec. Dens." on the screen) is defined as the weight (w) of the bullet in pounds divided by the square of its diameter (d) in inches: w/d^2 = pounds per square inch.

Copyright © 2003 by Bill St. Clair <>
All Rights Reserved