I found this design on easel but it is originally from here. I tried to cut it and build it with some hiccups. Now I’ve shown it to some people and actually have some demand for them and wanted to optimize it where possible.
The actual build is time consuming due to gluing all the layers, but not complicated. I modified the design I found since there were some errors and also tried to place tabs in areas that would make it easy to knock out with a chisel (flat spots where possible).
It is semi-automatic and you can load 4 rubberbands at once.
I’ve shared the modified design here here