Greetings Feanor,

Welcome to the forum.

Very in depth question for a first post. Comes up quite regularly but is very difficult to answer because "killing power" is so open to interpretation. There is quite a detailed article by Dr Robert Dohrenwend which comes up with a "lethality index" (can't remember if that's its actual name) comparing various weapons, but there is quite a controversy over the way the data is interpreted. There is even controversy over whether the wound inflicted would invariably be only percussive orpenetrate into the flesh, though I think the evidence is fairly clear that leaden projectiles at least did actually penetrate the bodies of their victims.

However kinetic energy and momentum figures are easily calculated once weight and speed is known. But most of us are enthusiastic amateurs without access to sophisticated speed measuring equipment, so accurate speed measurement can be a bit of a problem. The easiest method of doing this I know using only readily available equipment is to record the sound of the sling,  using a laptop computer or similar, over an accurately measured distance. (I usually use 10m as I assume the speed doesn't drop too greatly over that distance and the sound interval between the swish of the release and the whack of the projectile hitting the target is quite perceptible.) Then examine the waveform of the recorded sound using Audacity or a similar program to accurately determine the time interval. The release usually produces a slightly fuzzy wave but the hit gives a very distinct spike which is easy to place on the time scale. Average velocity over the measured distance is then easily calculated.

From my own and others measurements as well as observing the many video clips of slinging on YouTube it appears that anything over 40 m/s, especially with so heavy a projectile is very good. Anything over 60 m/s would be excellent, over 100 m/s would be Larry Bray's record distance type speed. I don't know if his speed has ever been measured but his record of over 437 m was established with a stone of around 2 oz. You will find that personal preference for what consitutes the ideal weight varies a lot. Many throw 150 g or more whilst others use very light weights in the order of 20 g or even less. Tennis and golf balls are very popular ammunition weighing approx. 56g and 45g respectively.

Hope the above has been of assistance.

Regards,

Aussie

Measuring the kinetic energy of sling shots is very easy. All you need is to have it on tape to make your calculations.
Foe example, if you know your 100 gram projectile takes .15 secconds to reach the target at 10 meters 10/.15 equals 66.6 meters per seccond.
From there, you can obtain kinetic energy, I always use the link below.

http://www.csgnetwork.com/kineticenergycalc.html

Speaking of, sling shots can indeed have as much kinetic energy as some modern firearms, but this energy does not translate into deadliness. A bullet is more deadly because of their faster velocities and smaller size.

Fëanor wrote on Jun 10^th, 2009 at 4:05pm:


It was explained to me by Aussie that kinetic energy the same in this two scenarios: A high caliber riffle bullet and a truck moving at 5 kph. They both have the same kinetic energy, but the bullet, with it's low mass and high speed kills and the truck's big mass and low speed would only push you to the side. No event is more powerful than the other, it's how you apply such energy that counts for killing power.

What we need is some kind of test. Me and my friends are trying to decide what to use for simulated flesh and we have a strong candidate, one type of squash. I have seen it, touched it and It's very close to the density of flesh. The other choice is a watermelon, but we're about to discard that idea, the squash is more consistent.

The only time there's been a test of a sling shot to a head replica was on that show Deadliest Warrior, they fired a glande and it got stuck inside the skull. David's shot at Goiliath was done with a rock, it would be intresting to see the same test with the rock, to see what happens.

Firing lead glandes and rocks at the body is something that should be tested on a side of pork, like they do with archery or atlatls. you can't beat the realism of such test.

And yes, I understand why bullets kill. Apparently, when you list the ways to efficiently kill a human, penetration of the organs is among the best. The very fast velocity  and penetration of the bullet destroys internal organs. 

Rockman wrote on Jun 10^th, 2009 at 7:37pm:


On deadliest warrior they slung what looks to be 5-7 ounces of lead at 91 mph, if you doubled (or almost tripled) the speed and used a 4 oz rock, then it would most likely be way more penetration.

But the denser material lead would still be best for penetration, 4 oz lead ball or, to take extremes, 4 oz depleted uranium ball would be even better with the doubled or tripled velocity mentioned.
Ballistics is difficult enough so with the added difficulty of having it affect a body with large variations depending on where you hit it seems to make it a lot easier to rely on empirical data.
Easiest would be to use live pigs and just see if the hit kills it but I am not tempted, dead pigs adds the difficulty of assesing if the hit would kill in cases of torso hits.
How do internal organ´s properties change in death?
Reason i pose the question is would say a hit on the spleen that is sufficient to rupture it on a live animal through blunt force also rupture it on a dead animal? Or damage a liver etc.

Feanor, have you made a "first sling" yet?

If so, what kind did you decide on?