Neat suff you all have done.
I built a lot of things for non-gunsmith application. Things like flywheel removers, etc. I do a lot jigs & fixtures at work. My two favorites were a tool to disassemble freewheels on bicycles and a tool that would make a whole roll of wire into a stack of wire that was bent, measured & cut.
About the only thing I did was make a bore guide for shotguns using an empty shell. The shell is of the 1 piece design. No big deal & not an original thought. It does keep the rod from scraping. I doesn't need to seal as the barrel is removed. I was too cheap to buy a bore snake for shotguns.
Nothing hard core like what y'all do.
Later,
WNTFW