Elementary ballistics question from a dummy.

[sportmuaythai]

Energy table for rifle cartridges are simply shown as foot pounds. I was told that it is foot pound per square inch. So what is the real answer, simply foot pound, or foot pound per square inch?

 

[Jay Kyle]

This is a good question. Foot-pounds is generally a measure of rotational torque - so could we say the bullet has so much rotational torque?

For a known bullet in flight, we have velocity, mass, frontal area, angle of frontal area - we should be able to calculate impact pressure in psi, and momentum. I think with all of this we should be able to calculate total kinetic energy.

The trick is to take these values and translate them into lethality - many folks have tried it over the years - but each formula is imperfect. Over time I've fallen into using the Optimum Game Weight-Big Game method solely because it was easy to use and seemed reasonable - but again I use it only as a rough approximation.

Jay

 

[sportmuaythai]

Thanks Jay. I take the figures as rough indicator of how powerful they are compared to other bullets of same type, but in different weight and at various ranges. Mean while, I await others to chime in.

 

[Lefty7mmstw]

Foot-pounds and pound-feet—what's the difference? | Mac's Motor City Garage

http://en.wikipedia.org/wiki/Pound-foot_(torque)

http://en.wikipedia.org/wiki/Foot-pound_(energy)

pound- feet is torque... angular momentum or a vector

ie you are pulling with 100# of force on a 1 foot wrench handle

foot- pound is a simple unit of work... ie. the force it took to lift one # one foot.

so your 243 has as much muzzle energy as a Volkswagen lifted one foot over said target. The only difference is the footprint the force is exerted on.

 

[Jay Kyle]

Thanks Lefty,
That helps fill a gap in my knowledge!

Jay