Mortal Weapons vs Monsters

We all know that bronze, gold, silver and Stygian iron will kill monsters on contact, no matter where the contact. But what happens if you tried to use a gun (metal rounds) or a steel blade on a monster? My hypothesis is that whatever you shoot or hit with will still harm the monster-it's effects though will be dictated by where you hit the thing and how powerful your weapon is, as opposed to a celestial bronze instant kill.

Stygian Iron, Celestial Bronze, and Imperial Gold are the only ones that kill monsters. It think that other objects can harm the monsters in one way or another, but they won't be nearly as effective as Stygian Iron, Celestial Bronze, and Imperial Gold. That's my guess.