Two ropes were 3 years old and the other two were 5 I think. That might explain something.
I can get nylon, but just to make sure, is there anything better and within a reasonable price?
I think I'll pass on using sinew right now. I have zero experiance with it and I don't know were to get it in my area. I'll save it for a later project.
Thanks for all the info.
FYI. My frame doesn't seem to have any flex anymore. When I first built it, that was a real problem. My throwing arm is tapered, light, and strong. I'm not sure what wood I am using but it is working for this sized project. I'm using a sling at the end instead of a bucket. Nearly put a hole in a barn with a golf ball at 100ft. The sling released way to late and gave a very low trajectory. When I made the adjustments and began to cock the arm, that's when the ropes broke. I guess this would really be called a torsion trebuchet because I yet to put the uprights on the frame. That will be todays project I think.
To funslinger: An onager is a catapult. And you are correct, it uses twisted cables to store the energy.