I don't think its stupid at all, no more or less stupid than any of the people who create makeshift gadgets that perform a similar task to something you could buy off a store shelf.
The problem is that there seems to be a lot of pussies who balk at the sight of a firearm.
Incidentally, a makeshift shotgun isn't nearly as dangerous as you'd think, so long as the barrel is of the proper schedule and has mechanical properties that would permit its use.
Its probably a 50/50 chance he didn't consider that, however being the nature of a shotgun, there's far greater danger in custom reloading one's own munitions than anything else.