This type of firearm features two barrels stacked vertically, one above the other. Firing is accomplished through separate triggers or a selector mechanism. An example is a sporting clays firearm where the user might want to quickly select between a more open choke for close targets and a tighter choke for distant targets.
The configuration provides a clear sight picture, balanced weight distribution, and allows for quick follow-up shots. Historically, it represents a refined design evolution, favored in competitive shooting disciplines for its precision and reliability and hunting, where the user can take advantage of more than one choke for different range shots.