Note: this page is entirely self-contained. It requires no server-side code to operate. All the computations are done by JavaScript code embedded in the HTML. If you "Save As..." in your browser, you can run it off-line.

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 this 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." above) 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.

I used Remington ammo for the preset buttons only because the ballistics were easy to find on the web. I handload or use military surplus for most of my shooting. You can fairly easily change the <button> tags for your favorite loads.

Muzzle Energy for Palm is a Palm handheld organizer version of a subset of this page's functionality.
iPhone Muzzle Energy Computer is a version of this page formatted to fit on the screen of Apple's iPhone.

Copyright © 2006 Bill St. Clair
Copying and reposting allowed as long as this copyright remains intact