I LIKE it !

Zip guns have been around forever they were a big thing in Chicago made with old hollow car antennas that were used a lot was the story, never messed with one myself. Mostly popular with gangs 50 years ago.

the way I was shown how to make a zip gun by a Brooklyn native I met in the Air Force, was with a car antenna section, a dead bolt door lock, and a piece of inner tube. a small wooden block tied to the innertube rubber band struck the dead bolt that struck the 22 shell. You pulled back on the block kinda like shooting a sling shot

interesting they are even making the case and projectile
I think muzzle loader would have been easier but sure

as long as we are on improvised you should like this one
ok edited I watched the video further and realized it has a bit of language @#$%^&*() so took it to just a link
https://www.youtube.com/watch?v=3YE9J7qcj0c

Geeze I learned how to do that 22 zip gun when I was in junior high. Isn't it or wasn't it illegal to posses one? Can't recall.
I know in highschool I got a hold of a copy of the Antartist Cook Book. Think it had zip gun and all the other fun stuff weren't supposed to play with.

Mac

a pistol needs to have rifling , and a rifle needs to have a 16 inch barrel

a 16 inch barrel 22 rifle can have a smooth bore but not a pistol

so it puts you in NFA territory if you get your length wrong so not illegal to manufacture just illegal to not register/ pay the illegal tax on it. if you make it too short .
illegal tax or not the tax man wants his pound till someone ends the illegal taxation

I led a sheltered life I guess. Cars dont even have antennas like that anymore. Have to steal a piece of pipe from the hardware store instead.

Danny
Pipes were for making bombs. LoL I believe there were also some metal ink pens that work too. Just need to look around see what is available. Maybe reforce the tube a big with tap. Back in them day was friction tape the go to now would be duct tape.

Mac

These were actually manufactured pre 68 needing no SN# but from an improvised design
still very possible today and if you made sure to have the barrel >18 inches would be legal

Geez I made mine out of 10 inch Cold Rolled Steel Tube. Then I drilled a hole for the cannon Fuse. Then I put a piece of 4 inch solid round Bar stock in the end and about 3 inches of weld then ground it smooth and welded another few passes around the seam. Then I mounted it on one of those old Ford Twin I beam Front ends. It shoots a Soft Ball wrapped in a Shop Rag with about a can of Pyrodex Powder about 600 yards.

When we need one of these legal will not matter.

Potato guns are always fun too.

In a total survival situation a trip wire can be set up to activate the trigger.

I'm talking about for animals, for food only, of course

along those lines a small muzzle loading shotgun/device because then none of the nfa rules apply and with and open cylinder barrel and no need to worry about fit just a large shot with a wad under and over