Man fed up with package thieves rigs box with shotgun blanks to stop them

Actually - no, not permissible - there is an old Iowa Supreme Court case which is illustrative, Katko v. Briney, 183 N.W.2d 657 (Iowa 1971).

Briney rigged his house with a spring loaded shotgun to defend against intruders. Katko entered with an intent to steal, set off the shotgun, and was injured badly enough to require hospitalization. He sued Briney for causing his injuries, and the Iowa Supreme Court sided with him, holding that it is impermissible to defend mere property with deadly force.

Although a landowner has no duty to keep his property safe for trespassers, he may not set deadly traps to ward off trespassers.

This modern day man with the empty shotgun shells would be held liable as well, if his traps injure anyone, even a thief trying to steal the packages.