Cedutus

You have to complete Serafen's quest to get another blunderbuss with the same passive named "Fire in the hole" It's pretty easy quest for an awesome weapon.

I'm running Spellblade with dual blunderbuss (Fire in the hole and Hand mortar), the modal ability on blunderbuss inflicts flank on self and gives you the streetfighter recovery buff. My battles are basically my buffing myself with Infuse With Vital Essence and Deleterious Alacrity of Motion, and proceeding to blast groups of enemies away with Full Attacks using Crippling Strike.