Dragon Pistols are finely-crafted firearms, the first of their kind, made by the Shuul for the Killraven Gang.  Typical of Shuul items, they are made to be beautiful as well as functional.

Each is constructed primarily of Black Adamantine, making them impervious to magic.  For example, a Heat Metal spell would not work on the weapons, and magical fire would not cause risk of their loaded ammunition exploding.  

The weapons are capable of holding four rounds of ammunition at a time.  They are also built with a self-destruct mechanism to prevent them from falling into enemy hands, which can be activated by trauma or set off manually.

Phen knew of five Dragon Pistols in existence, one of which he currently has, one more you confiscated and gave to the Longfinger's Guild, and one more was destroyed by its wielder during your fight with them in the Guildsman's District.  He also knows they have the supplies to make more, but making each one (and their ammunition) is non-trivial.