# Crazy Question



## mostho (Mar 28, 2017)

Well I have tons of rubber from my spearfishing gun 14mm / 16mm / and 18mm diameter
Wondering if these can be used as engine.

Honestly I can see that they can have a limited stretch (but lot of power) compared to band or small diameter tubing. But using some hi tec cordage like Dyneema or Kevlar cord that I have I for instance use 10cm of rubber and then rope. A mixed. It is used also in several spearguns.

For instance a 14mm rubber streched at 300% can hold 20kg of force. Using less rubber or lower stretch factor can lead to a less powerful shot. On the opposite.

If they can send straight a 500gr shaft inside the water, probably only 5 to 10cm of this rubber with the remaing legth of cordage can do a lot for few grams of pebble or lead or whatever.

Comments are welcome? Too much crazy idea?

Im going to ask but and to test also in my wooden home made Y

Ok found some replies in the forum....


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## romanljc (May 26, 2014)

Big powerful tubing needs . Big heavy ammo good for hunting but less acurate. 
è meglio usare qualcosa più leggero


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## mostho (Mar 28, 2017)

Something lighter is better I know.

Just imagination to find more uses of my rubber bands.

For instance.

So far the calculations used for spearguns are sometihing like gr of rubber/kg force.

So far 7cm of 14mm bands can be enough to propel to 2 kg and more. Adding the remaining length of the band with simple hi stregth cordage. It's called like a "fusion"


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## mostho (Mar 28, 2017)

I think I need to draw something... to better explain


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## MikmaqWarrior (May 12, 2014)

Would be great for a slingbow, I bet

Sent from my B1-770 using Tapatalk


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## mostho (Mar 28, 2017)

Something like that?
As far as I know its this will have a more reactive thrust rather than a progressive thrust as the more common bands isn't it?


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## romanljc (May 26, 2014)

The only way to know for sure is to try them out use something like 1/2 inch steel ammo or anything heavy like that .


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## mostho (Mar 28, 2017)

MikmaqWarrior said:


> Would be great for a slingbow, I bet
> 
> Sent from my B1-770 using Tapatalk


for a slingbow its really powerful and more appropriate probably but worth to experiment... maybe?


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## mostho (Mar 28, 2017)

romanljc said:


> The only way to know for sure is to try them out use something like 1/2 inch steel ammo or anything heavy like that .


cnsider that 40cm of band elonged to 300% of the smallest diameter (14mm) can have 30kg of thrust and can propel 400gr shaft into water (800 times more dense than water)

I have to find some time and a good Y


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## MikmaqWarrior (May 12, 2014)

mostho said:


> MikmaqWarrior said:
> 
> 
> > Would be great for a slingbow, I bet
> ...


Joerg Sprave used spear fishing tubes on some homemade slingbows made of multiplex...They worked great...Check him out on YouTube

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## mattwalt (Jan 5, 2017)

It seems its more the active length/draw of the elastic where the power comes from and not so much the strength of the rubber. So longer and lighter pull is better than short heavy - but needs to be matched to ammo anyway. You'll need to try and see what can work.

It may be interesting to change the dyneema out for elastic - and effectively make pseudo tapered tubes... firing some pretty heavy projectiles...

Like MW mentions above - probably work great on a slingbow.


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## mostho (Mar 28, 2017)

mattwalt said:


> So longer and lighter pull is better than short heavy -
> 
> It may be interesting to change the dyneema out for elastic - and effectively make pseudo tapered tubes... firing some pretty heavy projectiles...


nice


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## romanljc (May 26, 2014)

mostho said:


> romanljc said:
> 
> 
> > The only way to know for sure is to try them out use something like 1/2 inch steel ammo or anything heavy like that .
> ...


This may be a crazy Idea maybe you could split the big tubes in have don't no if it can easily be done you would have to test first on a scrap Part first


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## Imperial (Feb 9, 2011)

But will you be able to pull it?


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## raventree78 (Apr 20, 2016)

This guy did something like what you are talking about.


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## mostho (Mar 28, 2017)

raventree78 said:


> This guy did something like what you are talking about.


got it!! very similar.

Still not using 14mm rubber bands


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