Auburn Man has guns confiscated. Related to the Worcester incident.

[Rob Boudrie]

Potato canons have been called infernal machines .

There was a case in Holyoke a few years ago where the DA tried to prosecute someone for carrying a firearm without a license, to wit a spudzooka. When the court ruled it was not a firearm, the prosecution argued it was an infernal machine and the court ruled it wasn't one of those either.

Well, at least that is somewhat sorta related if the cannon was an exothermic type.

The most common form of spudzooka uses the ignition of an aresol sprayed into the chamber - most commonly hairspray, but WD40 works nicely as well, thus meeting your exothermic requirement. I don't know the detonation velocity of the propellant, so I cannot say with certainty if we are talking deflagration or detonation, but I suspect the former.