Not to mitigate the lack of forethought of the amateur bomb maker, but:
"Anything that goes `bang' is illegal,"
Guns go "bang". Black powder cannons go "bang". Lots of stuff goes "bang".
$300 outta get you a purty good old Smith and Wesson, Ruger, or Taurus revolver.
$150 outta get you some beginner's shooting lessons.
His possibly illegal explosives and hospital trip probably cost at LEAST that much.
It will probably cost him the right to buy that gun, now. The fact that his only victim was himself might keep him out of prison, but I don't see him avoiding felony charges.