[Eye of Unk]

For what they had in mind I would have just built a big plate with smooth seamless tubes and a firing pin receiver for each one. All you need is an 18” tube, two dozen would work, some plumbing parts, actuators to select which tube to fire.

[Pontiac]

I agree with you guys that for what is being accomplished here an over sized zip gun would be sufficient.

But actually doing so would put you in the cross hairs (oops can I say that) of the BATF.