let me introduce myself first, I am Jörg Sprave, 46 years of age, a German. I run "The Slingshot Channel" on youtube, a hobby I am very proud off. Now that Ivo (whom I met before on another great forum - Hi Ivo!) has officially declared rubber to be an established energy "source" for crossbows, it seems it is time for me to start posting here.
I have designed and built many slingshot crossbows in the last few years, but here are two designs that work really well.
First, my "medieval style" crossbow - with draw weights of up to 200 lbs, a mighty strong ball shooting weapon.
The lock is a modified "rolling nut" that can accomodate a 19mm (.75") lead ball, large musket ammo in fact.
I use spear gun rubber for it, quickly interchangeable.
Here are two videos about it:
With 100 lbs bands, no scope:
200 lbs, at last:
The other model is not fully finished, but well on its way.
Slingshot crossbows are fascinating weapons. Powerful enough to be lethal (>60 ft-lbs), easy to make and very accurate.
However, all of my power sling-x-bows were pretty long. That is, until now!
I built a bullpup crossbow, with rollers that extend the draw. This has a stirrup and can therefore be cocked with both hands, allowing very strong bands.
Here you see it in comparison with an earlier model of mine:
In this video
you see it shooting triple TB gold bands per side, the maximum I can draw on a conventional slingshot. But the photos already show it with six layers per side, it shoots a 20 mm steel ball with more than 230 fps - well in the 60 ft-lbs realm commonly stated as "lethal".
I will do some more sanding, add a front handle and a scope, plus a nice paint job.
Will make a how-to video (tutorial) for next week! Stay tuned.