They are not a "firearm" as they do not shoot a projectile. State laws vary. There is a fellow who rebuilds them for sale ,not cheap. They are ,however,regulated by Federal Law regulating any pressure vessels.
Worked with pressure vessels for a few years(NASA,JPL) and would NOT want to wear an old steel bottle on MY back ! Would not want to be anywhere near one being used ! No matter what was done to inspect the rebuild the possibility of a failure is there. It would not be pretty :shock:
I believe that a mess of the old WWII era ones were surplused to the US forestry department to us in back firing, they were found to be overkill. They did however, when filled with water, make the ultimat "super-soaker" for hitting fires in standing trees :grin:
Any of you vets remember all the fu-gas stuff, aiming a hunk of 6" sewer pipe or whathaveyou at your suspected enemy approach, throwing a detonator down the barrel, mixing up the napalm, pouring it down the barrel and waiting...FFFOOOOMMM, Bad Ass Stuff, remember "Napalm sticks to Kids". Have any of you heard the legend about mixing Tide soap with gasoline to make napalm, it was a soap like powder that was poured into the gasoline.
I would not want to be anywhere near anyone carrying a pressurized container of fuel on a battlefield, it proved invaluable from the sense that if an enemy is buried in a hole in the ground you can remove all the oxygen from his lair and roust him that way, otherwise for the amount of weight, explosives in the manner of anti-personnel grenades are probably more efficient. A grenadier would be more effective IMHO, white phosphorous/thermite is as deadly as napalm anyday and it burns underwater.