That’s a solid idea about using the screw-off cap to spray hairspray directly into the back end of the cannon. To make sure the hairspray stays contained, you could also try using a rubber seal or gasket around the cap to prevent any leakage. Another suggestion is to lightly tape or seal the openin...

Honestly, small-scale metal casting feels way too technical for most folks to pull off.

Isn’t 30 hours a bit rushed?

Air intake valves and hammer pin valves.