Crossbow/mechanical marblegun/harpoongun

[Brian the brain]

This design has been discussed before so I decided to post it here for all to see.

I've built this a long time ago.It shot a marble halfway into a solid wood door.Half of the marble was in I mean.Glass jars where fun to shoot.THey blew apart in a cloud of glass.

The advantage is, you can easily repeat shots and the gun is silent.

Disadvantage is the accuracy.
The pulleysystem I designed doubles the distance you can pull the string therefor doubling the speed but halving the power.So I just doubled the amount of rubber bands to get it back up to my maxcimum pulling force.Well not maximum but to the point I started doubting the structure would hold.I estimate it took about 40 kilograms of force to pull back the string.
Still my pneumatic gun is more powerful.(over 300 psi)
This design would work with a strong spring( or a number of them) aswell.

Without the upper aluminium strip it would be just a harpoon gun.This would be much more dangerous because of the projectiles weight and pointed shape.Accuracy wouldn't be an issue anymore.

If anybody is interested in copying this design or modifying it, I offer my help.(pretty proud of it)

[Benny]

great trigger design brian, turns out im making a crossbow, im about 2/3 through it.

[Brian the brain]

The trigger is very smooth.If you shape the upper part of the "catch" less dome-like it will automatically fall back when you pull a string past it.Attach a spring to it so it wants to stay in the protrayed position and it will automatically lock too.

[Atlantis]

I built one of these out of KNEX with rubber bands and yarn just to get a feel of how it works. I hope to make a full sized version out of wood and nylon string. What string did you use for yours?

[Brian the brain]

Just some black string I bought at a hardware store.Nothing special.Looked like a very long shoelace.Be sure to buy more then enough length.It's hard to tie a knot in the correct place at the first try.I made a small pad out of tape in the center to keep it from slipping over the marble.It worked only occasionally.I later cut a small section of electric pvc pipe and drilled a hole through it sideways and slipped it over the string, so it would "grab" the marble with the front.After all these years I still wish I never scraped it.I should have converted it to a harpoon gun.Never did...

[Flinchy]

interesting design you have there. i myself have been thinking of building my own fully functional crossbow, rather than one that just shoots marbels.