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Summary

To summarise, don't try it; it's a fool's errand. Stick to smooth lead or steel round ball if you can.

Disclaimer

Don't do it. It's dangerous and there's no point as far as I can tell. If you ignore my warning and go ahead anyway, you'll probably hurt yourself or someone else, break something and might also go to jail. All slingshot activities are dangerous and even the shooting or regular ammo should be done with competent supervision and with adequate safety glasses. No matter what, I will not be held liable.

Introduction

Long before I joined the forum I experimented a lot with ammo shapes. Let me tell you about it so you don't feel the need to do so.

It wasn't an abject failure. I was trying to shoot all sorts of things at one point, including spin stabilised darts and pub darts and deliberately unstable shapes. I can get an oval to hit consistently end on, as you can see from the example below. That didn't make it any more accurate or more ballistically efficient over target shooting ranges and it raised the danger level considerably. I shot from behind a Lexan full head and face shield and a big heavy desk and I used a slingshot rifle so my fork hand wouldn't be down range.

Water Grey Wood Liquid Balance


Why?!!?

The reasons why one might want to stabilise a projectile are:
  • Elongated projectiles have a better ballistic coefficient (low drag) - but drag is a miniscule factor in slingshots
  • Elongated projectiles have better penetration - but blunt trauma, not penetration, kills any legal small game
  • Pointed projectiles, such as a Filipino pana dart penetrate better - but are dangerous to shoot and a liability nightmare to sell
  • Expansion with a hollow point stops a very high energy projectile quickly - but this is almost certainly illegal in most places and you need a lot of velocity, even for fragmenting safety slugs.
Watch Font Slope Parallel Clock


In addition, pretty much every kind of stabilisation that I have tried significantly decreased accuracy, so I have pretty much given up on the idea.

The reason I persisted for so long is pure curiosity. I was also trying to shoot unstable ammo, to investigate the importance of shape and centre of gravity. It's not as important as you'd think over a short distance. Some people can hunt with fairly aspherical stones, but it's best to use round ball.

How to stabilise a projectile:
  • Yaw spin stabilisation (like a frisbee) works on discs, etc. but it requires a complex mechanism and probably a slingshot gun. That limits the market a lot.
  • Roll spin stabilisation requires an object to be longer than it is wide.
  • Fin stabilisation (like pub darts or an arrow) best works on long objects, but it can also work on round ones as you can see above. Fins can also make the projectile spin, but the casting required for that is very involved (spiralling fins on a stalk.)
  • Drag stabilisation, (like a shuttlecock, Chinese dart, Filipino pana, or Amazonian blowgun dart) is not very effective and can increase overall drag more than it saves. Air rifle pellets don't work well in slingshots. The void makes them low density and do the ballistic coefficient is bad and also they are supposed to be shot from a rifle barrel, not flung.
But how to make them?
  • It's hard to cast fins without a spincaster. The lead won't flow to the end of the fins.
  • It's hard but not impossible to make a shuttlecock style pellet.
Hard or labour intensive to make means expensive.

In the end, I think the most practical solution is to make an elongated oval (length 2 or 3 times the width) from lead in a two part mould with a screw thread core that matches a pub dart's shaft screw attachment. The shaft is useful as it increases the effect of the stabilisation without additional drag. You shoot the dart with the weight in the pouch and the shaft poking above. That's how I shot the sinker in the picture above. Note that you will also have to glue the fins to the shaft as cattys are so fast that the fins inevitably fly off the shaft.

Conclusions
  • Don't do it. It's hard to get right and easy to hurt yourself.
  • The more dense a projectile is, the better its ballistic coefficient.
  • The more dense a projectile is, the more resistant it is to instability. Oval sinkers work pretty well at 10m, though I wouldn't use them for very long range shooting.


Wood Hardwood Flooring Wood stain Water

zamarion
Apr 17 2012 01:48 PM

hmm i have been linked to this blogpost from my topic wich you can find here Weird Ammo?
the ammo i show is easy to create with a little bit of feeling for when al 3 fins are similar and its easy to shoot by a little longer pouch and holding the pouch just in front of the tip and shoot fast and with pin point accuracy
let me know what you think


Gesture Thigh Art Magenta Thumb

Chevas
Oct 30 2012 04:58 PM

What about the end of a drill bit? Perhaps spin would occur from the air if a slight amount was provided on release. Like spiraling a football?


Gesture Thigh Art Magenta Thumb

Chevas
Oct 30 2012 05:03 PM

Another idea may be an oval sinker, large hole, with a wood screw placed through the center. Would likely not work but I share your once held passion for improving ballistics. Oh, dimpling like a golf ball may help. Your likely correct though on performance improvement. It would be nice to have a projectile that improved accuracy, speed and range.
 
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