This post inspired me to make this. It don't look great but it shoots quite well. It's core is plain old 1/4 inch steel rod the yellow tubing came from a set of wally world marksman tubes. I filed the tips smooth then covered them in heat shrink tubing just to be sure. The slingshot feels a little weird at first but settles into the hand quickly.
Since I hurt my thumb in a motorcycle accident two years ago I can only shoot one SS without pain. Big Dan designed and built this one for me. I love it and while I miss shooting a variety of forks ( I have a few) I happy to be able to shoot pain free.
That is a very neat design and I am glad that you were able to find a way to keep on shooting