Saturday, June 04, 2005

The effect of gunshots

As far as someone flying backwards, through a window, etc., it's crap. Always has been.

What brought this to mind is an episode of 'Mythbusters'. They took a pig carcass, hung it up on a balanced mount, and shot it with various firearms to see if it would be thrown back. Nope. Not with a .308, not with a burst from an MP5, at the end either a 12-guage slug or 00 buckshot transferred enough energy to make it fall off the mount, but that's all; it did NOT go flying backward, not a bit.

Peter Capstick, in various of his books and articles, explored the idea of 'knockdown power', finding it to be crap. Bullets just don't work that way. A bullet penetrates, so the energy is used in pushing it through the target and(in the case of soft tissue) damaging the tissue. If you took the energy tied up in a .357 Mag bullet and put it into a steel plate, say, a foot square, striking a man it would be able to knock him backwards, but that's a whole 'nother thing. Capstick said that in his experience he'd never seen any animal of a size greater than 40lbs actually knocked over/back by any cartridge, including big express-rifle stuff.

I think that if you were talking about a shotgun hitting somebody at close(a few feet) range, that might be able to physically shove the target back, but that might be equally from the press of expanding powder gas as well as the shot. And it would probably have to be shot; a slug would penetrate, shot would be more likely to transfer its full energy to the target.

This is one of the reasons I don't really like L. Sprague deCamp. He's an author. I originally didn't like him because he 'edited' a lot of the Robert E. Howard 'Conan' stories, and his 'editing' often involved rewriting the damn thing. Then, he wrote some short stories collected in a book called 'Rivers of Time', about a guy running safaris back in time. In the first story the character Rivers is laying down the law, saying that if you want to go back and hunt dinosaurs the only rifle you'll be allowed to carry is a .600 Nitro Express, because it's the only gun that can knock a dinosaur down. Which is followed, in at least one of the stories, by description of a dinosaur being knocked off it's feet by the impact of a shot. Besides messing up the stories for anyone who does know anything about guns, it spread bad information(done by a guy who's supposed to be serious about science).

Oh well. Now I can just wait for the next 'investigative report' from some idiot journalist who doesn't bother to find out that 'assault rifles' aren't any more powerful than anything else. Oh well.


Dave said...

Well, I'm going to nitpick a little bit. When it comes to shooting something solid and moving it, KE alone is very deceptive.

The important factor is momentum, which is p (momentum) = mv, whereas I'm sure you know KE = .5mv^2. So if you take a 115gr 357 magnum vs, say, a hot 45 ACP with a 230gr bullet--both carrying the same kinetic energy--the 45 ACP will knock the object back more because its KE relies more on mass relative to the 357 magnum, yielding a higher momentum.

All that aside, it would take a damn powerful shot to move a 165 pound man more than a few inches even if you could apply the force to his body without any penetration. Equal and opposite reaction and all that...

Firehand said...

Oh, yeah. All things being equal I'd rather depend on a big heavy projectile than a small light one.

My big gripe is with the crap of people flying backward, through windows, etc., when hit. Or animals being physically knocked over.

Dave said...

I never realized what kind of peashooter my 9mm was until I got a case of 45 ACP and held a few of those cartridges in my hand... haven't shot more than 100 rounds through my P95 since I got my 1911.

Yeah, movies and books just jerk me right out of the story when people start flying unless it's intended to be exaggerated, with 'wire-fu' martial arts and such. I've actually started tuning that out and gotten a lot more annoyed with, for example, the multiple-click sound effects on an empty... single action weapon. Argh!

On the gun scene, it kills me when people start claiming that the velocity of lighter bullets will cause the kind of damage light rifle bullets at mach 2.5 cause; for a handgun, the heaviest possible bullet with an acceptable trajectory and case pressure is the way to go.