The building was originally two separate structures, one a two-storey Shifting House (for the inspection of incoming gunpowder) and the other a Cooperage which later became another Shifting House). The main Rolling Way of 1804 opened to B Magazine through a broad arch.

B Magazine, part of the Priddy’s Hard complex, comprises a group of structures related to the operation of A Magazine. Built in 1775, it underwent various alterations and additions over time. Originally consisting of two detached rooms – a cooperage and a shifting room – it later became a continuous range parallel to A Magazine, joined by a central link building. The exterior of B Magazine reflects its complex history, with brickwork in English bond and a slate roof. Originally two separate structures, it evolved into a unified range by the mid-19th century. The east side incorporates the original traverse wall to A Magazine, showcasing variations in treatment and walling over the years.

The main Rolling Way, constructed in 1804 and rebuilt in brick in 1825-7, serves as a crucial link to B Magazine. Adjacent structures include the foreman’s office, shoe room, and shifting room, built at various times between 1804 and the late 19th century. Internally, B Magazine features plank floors, square posts with bracketed caps, and painted brick walls. The king-post roof trusses support one purlin and close boarding, reflecting the building’s functional design.

B Magazine represents a tangible link to the operational history of Priddy’s Hard and its importance in supporting naval operations.