Since 1675, the company has been located at the London Proof House on Commercial Road, just east (outside) of Aldgate and the old City walls, in Whitechapel.

Although modern non-destructive inspection techniques enable the examination of the internal structure of metal to a high degree of accuracy, there is still no better way of determining which weaknesses and imperfections might prove dangerous to the user.

Unlike many livery companies, the Gunmakers have retained an active link to their trade and consults with the government on related firearms regulation.

If they have maintained structural integrity, they will be stamped with proof marks indicating the test pressure, bore diameter in millimetres at 9" from the breech face, chamber length, suitability for use with steel shot or not in the case of a smoothbore shotgun, a date stamp or code and the mark of the proof house that tested the firearm (London or Birmingham).

De-activation of firearms is a process where the gun is altered in such a way as to render them permanently incapable of firing and thus completely safe for collectors.