From my diving days, I vaguely remember someone with just such a device. It was commercially produced.I'd consider making one simply charged with about twenty cubic feet of air compressed to 3000 psi like a dive tank. Jab a big needle in and then hit the trigger and fill them full of air.
This was not for underwater use it is for pulling an alligator up and dispatching it or if one suddenly woke up in the boat and decided to eat everyone.stand watie said:Charlie Petty et.al.,
fyi, "regular firearms" don't work very well under water, especially at deeper dive distances.
fwiw, the IDIOTS/thugs of BATFE don't seem to care about "shark-killers" for UNDERWATER use, provided that the devices are NOT "concealable".