# Why do slingshots so well in ballistic gelatin?



## JoergS (Dec 17, 2009)

My gelatin tests are very successful on youtube. I must say that I never expected such great results beforehand.

Then I was asked by German TV to make a huge block of gelatin for a comparison of a longbow against a musket. The musket ball was a 3/4 inch lead ball, travelling at over 500 m/s. It lifted the 160 lbs block 4 inches off the table and the impact looked spectacular in slow motion - but the ball did not go through the block, penetraded about three feet maybe.

The lead ball was massively flatened.

Then I tested the slingshot, same ammo. I shot the ball through the entire block! Strange.

Then I saw a Mythbusters episode where they tested firearm shots into water. The muzzleloaders did best! Even the .50 Browning was weak in comparison - the bullet shattered on impact and was harmless after one foot.

So slow and heavy does the job! Gelatin and flesh both contain 80%+ water, and the impact of a fast bullet onto the surface of the water creates massive resistance, the bullet spends most of its energy at that point.

It works like jumping into a pool, from three feet it is easy, from 10 yards it is painful and from 30 yards it is outright dangerous, the surface feels like concrete.

I believe that this is true for real body hits too. Once the bullet has penetrated the skin, it travels very easily through the tissue, only bones will stop it eventually.

Interesting!

Jörg


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## USASlingshot (Feb 25, 2010)

thats pretty cool!


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## jmplsnt (Jan 1, 2010)

I can't say I have ever shot a block of ballistic gelatin with the mighty German "W" but I have bagged a few of what I will term "ballistic bunnies" in my time. Using lame storebought tube sets and hand-cast lead round balls I shot completely through every rabbit I ever killed. I have never recovered a round ball from a rabbit regardless of the range.

You are exactly correct when you state the ball wastes most of its energy on impact. The slower slingshot doesn't and therefore is free to continue on its glorious and devastating course.


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## hawk2009 (Dec 30, 2009)

Mythbusters great programme love it.


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## Bill Hays (Aug 9, 2010)

Think along the lines of non-newtonian fluid... there it is, same principle!


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## keeco (Feb 28, 2010)

try it at 100 meters


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## ZDP-189 (Mar 14, 2010)

JoergS said:


> I believe that this is true for real body hits too. Once the bullet has penetrated the skin, it travels very easily through the tissue, only bones will stop it eventually.
> 
> Interesting!
> 
> Jörg


I agree. Hitting the quarry with a slow dense ball is like stabbing it, compared to a high velocity round which is more like exploding it.


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## ZDP-189 (Mar 14, 2010)

If you're considering whether large or smaller calibres will penetrate better you must factor in:

Mass, increases to the cube of increase in calibre. Frontal area increases to the square of increase in calibre. The nett result is bigger balls have better penetration for a given velocity, shape and density.

OTOH, if you shoot a big and small lead ball from the same bandset, a heavier ball will fly slower. This is not proportional, because for a larger ball the bandset will be more efficient, especially if the bandset's strong and the laden weight is close to the dry-fored weight.

Therefore, yes, larger calibres should penetrate better (and lose less velocity on the way to the target), but how much so depends on the bandset and the relative mass of the shot.

What is more interesting is denser materials penetrate better.

Being able to control penetration is most easily accomplished with the shape of the projectile (tip shape and frontal area/inertia) and the way the projectile deforms, expands or tumbles within the target. In order to do that, you must stabilise the shot orientation in flight. Presuming spin-stabilisation is not possible, then the remaining options are fin- or drag- stabilisation. This was the purpose of my research some years ago. It is possible to get a shot to hit end on without adding much drag. Therefore you can make a bullet tumble, expand or penetrate as you wish.


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## JoergS (Dec 17, 2009)

Made the first video in the new garden today. Shot at a supermarket duck, still in the plastic coating. Used 16 mm lead balls and both the Novitzkenegger and the "W" in Butterfly.

Both setups shot clean through the bird, even lengthwise. Penetrated the skin in and out, broke the spine and the bones.

I have no Dsl internet, just my ipad and 3g, so I cannot upload the video... tomorrow, hopefully. Shots recorded both in hd and in 1200 frames per sec.

Jörg


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## dragonmaster (Dec 24, 2009)

Now Ive jumped 15 feet to the ground "in my younger days" but it still was no bed of roses and Ive dove 50 feet " my highest " into water yes the water was deep enough with no pain at all went down pretty far so would the shape of the projectile make a difference.


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## Dayhiker (Mar 13, 2010)

Very interesting thread. . .
On a more intuitive level, I was shooting some steel balls at tin cans (10 yds. distance) the other day, using single tapered thera gold. I usually like penetrating the cans with 3/8 balls. But I sent away for some 1/2" balls recently. When I took the first couple of shots, I was surprised at how slow they flew from the pouch, and I thought "these would never do for hunting with this band set." But on the third shot, I hit the can square and was shocked by the big hole it tore into it! Wow! . . . I concluded that there is something to be said for the inertia of a denser ball flying less fast.
Or something like that.


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## whipcrackdeadbunny (May 22, 2010)

ZDP-189 said:


> If you're considering whether large or smaller calibres will penetrate better you must factor in:
> 
> Mass, increases to the cube of increase in calibre. Frontal area increases to the square of increase in calibre. The nett result is bigger balls have better penetration for a given velocity, shape and density.
> 
> ...


What would we do without you? Have you seen the soft foam American footballs with flights? there is potential ammo there, a nice slow flight, yet even and possibly a sharpened tip.


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## ZDP-189 (Mar 14, 2010)

Footballs with flight? I was trying to make a lead Vortex Football when I made this:










This above stabilisation was in only 10' of travel. It's a good proof of concept.

I never did get it to spiral accurately like an Aerobie, though.


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## whipcrackdeadbunny (May 22, 2010)

ZDP-189 said:


> Footballs with flight? I was trying to make a lead Vortex Football when I made this:
> 
> 
> 
> ...


That's almost exactly what I had in mind, save a smaller flight, surrounding the main body, I think I remember seeing this photo before; yes, we were talking about a dimpled ball, for optimum flight. How about fins, which spiral round the main body coming almost directly to the tip and pushing over the tail by a little?


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## Sam (Jul 5, 2010)

ZDP-189 said:


> If you're considering whether large or smaller calibres will penetrate better you must factor in:
> 
> Mass, increases to the cube of increase in calibre. Frontal area increases to the square of increase in calibre. The nett result is bigger balls have better penetration for a given velocity, shape and density.
> 
> ...


Two words guys - ballistic coefficient. Oh and looking at the history of the hollow point bullet may also help you...


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## Sam (Jul 5, 2010)

Oh and to add to my previous point resistance, both in mediums such as air and flesh compounds. To illustrate this point I'll use Kinetic Energy, where a similar phenomenon occurs with velocity. Now the formula for calculating Kinetic Energy, when using SI Units is:










As we can clearly see velocity is squared what does this translate to? Well that means that if there are two ball bearings of equal mass, and one's travelling at exactly twice the speed of the other one, the faster one will have *four times *the Kinetic Energy of the slower one! This is because 2[sup]2[/sup] = 4 (2x2 = 4). I won't bore y'all with fluid dynamics and ballistic coefficients - Wikipedia's much better, than me, at that! It can be a great cure for insomnia though believe me!


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## christopher (Jan 8, 2010)

This is not surprising at all.

Water posses a property of frontal resistance, I believe all liquids do. One of the reasons why it's insane to try to reduce the volume of liquid by physically trying to compress it. There just isn't much room for electrons to squeeze together. In Jorg's experiment we see that in the equation F=ma, that mass between a muzzle shot and a slingshot are the same and the only difference is acceleration. Well when you increase acceleration you increase the force, the opposing counter compression water becomes greater as an opposing force. So the slower the acceleration the less counter force you have.

So using the same mass and material, the faster and faster you shoot it, the less and less penetration you get. As long as you have momentum, the slower you go through a liquid the better the penetration you have. This is why people die jumping from hieghts into water. The water didn't kill them, it's their body's inability to counter the compression causes by water at high rates of speed. Cement has better compression rate than water.

Side note of physics: This is why the theory of if an asteroid is going to hit the earth, we have a better chance of surviving if we attach rockets to the asteroid and speed it up. The greater acceleration means the greater the counter forces against the mass causing the mass to slow down faster and break apart before it hits the ground. This is what most space debris already does.


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## christopher (Jan 8, 2010)

Another experiment that shows you impact resistance is shooting the children's toy Silly Putty. Either as ammo or as a target. It's nice and soft until it's hit at high impact. I amazed my son hitting the stuff with a hammer.

You can buy it in bulk for Dow Corning in 100lb blocks. Here is how to:
http://bulkputty.org/ordering/dow.html

Or from Crayola in smaller 5lb blocks.
http://www.crayolastore.com/product_list.asp?SKW=SILLYBULK


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## Sam (Jul 5, 2010)

Exactly Christopher, I believe that if you compressed the water enough, it would turn into Ice!


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## christopher (Jan 8, 2010)

Sam, I can tell we are kindred spirits.

I contend if you compress water that it would go from a liquid straight to a plasma and immediately produce a fusion reaction with the hydrogen, causing the oxygen to be immediately blown off in an explosion. Then the hydrogen producing a few heavy elements only to let loose a massive shockwave as it collapses with no gravity to hold it together.

That would require some really really strong flatbands. ( C :"


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