The double-barreled shotgun (Dunali SxS) is of the shotgun class and therefore has high stopping power.
It holds two shots per load, and 40 extra rounds for firing. Combine this with the Hellraiser class, and the gun can sort of be rapid fired if you are using the 50% reload speed perk.
It has extremely poor accuracy and range, so it is best used up close in tight situations where a primary weapon has run out and you need to get closing zeke off of you for a brief period. It isn't the best in swarms because in order to deal any significant damage the enemy must be almost on top of you, which isn't ideal.
The gun is still extremely powerful, and at close range it has the ability to take out multiple enemies with its two shots, but use them wisely and don't try to spam the shots. It should be noted that it can be silence, which is quite useless since you can alert other zombies by unintentionally hitting them with the widespread of this shotgun.