Ordered some speargun rubber.
Got 16, 18 and 20 mm thickness, a meter each.
The stuff is beastly! I decided to test the "weakest" one first. 6,5mm walls, compared to 3mm walls on the already tough Thera Tube silver. Here you see TB black, silver and the 16mm speargun rubber in comparison.
Did a bandset for the medieval crossbow. The center hole is too small and the rubber is too tough for the knot in hole method, so I attached the rubber to the outside. Works fine.
Draw weight of this exceeds the 40 kg my scales can measure. I estimate it at 45 kg (about 100 lbs).
I reinforced the nut and tickler with steel because I did not trust the wood on wood method for this off the scale power. It holds fine.
It is surprisingly easy to cock the crossbow, the stirrup method rocks. Ancient weapon makers clearly knew their stuff.
It shoots absolutely frighteningly fast. My most powerful sling-x-bow for sure.
But there is room for improvement - see the 18 and 20 mm beasts in comparison... stay tuned.
Jörg