Calamity

Calamity is a firearm. It has a 10% chance to inflict Poison when used by either Noctis or Prompto.

Source
Calamity can be purchased from Culless Munitions at the Wiz Chocobo Post and the Cauthess Coernix Station for 300 gil. It can also be found as a collectable north of the Post, near Ausace Haven. It can be sold back to shops for 150 gil.