The building was designed by John Horton and consists of a centre bay, emphasised by a segmental parapet, which contains trophies by William Hollins.

Its remit was to provide a testing and certification service for firearms in order to prove their quality of construction, particularly in terms of the resistance of barrels to explosion under firing conditions.

Such testing prior to sale or transfer of firearms is made mandatory by the Gun Barrel Proof Act 1868 (31 & 32 Vict.

c. cxiii), which made it an offence to sell, offer for sale, transfer, export or pawn an unproofed firearm, with certain exceptions for military organisations.

The Proof House still exists, largely unchanged in both purpose and construction, although it offers a wider range of services including ammunition testing and firearm accident investigation.