Typically, derringers fire only one barrel at a time. While some antique or custom-made derringers might exist with the capability to fire both barrels simultaneously, this is not a standard feature and would be considered highly unusual. The vast majority are single-action, meaning one trigger pull fires one barrel. Over-under double-barrel derringers often have two triggers, one for each barrel. Side-by-side double-barrel derringers usually have a single trigger with a selector switch or alternating firing mechanism.
The design intent behind firing a single barrel stems from the derringer’s primary purpose as a close-range defensive weapon. Accuracy at longer distances is not a design priority. Firing one shot accurately is considered more valuable than unleashing two shots simultaneously with reduced control and accuracy. Historically, the small size and concealability of the derringer were prioritized for personal defense. This focus on compact design often dictated single-barrel firing mechanisms due to space constraints within the frame and simplified operation under stress.