Interesting conversation with another Armourer of the era about the big 1.5" signal pistol. The redundant locking mechanism that ensured that the pistol was fully locked into the aircraft that I complained about was also interlocked with the main break-action lock. This same longitudinal lock ensured that the pistol was locked fully into the aircraft or AFV and at the same time, fully locked closed. Apparently, the last aircraft it was used in were the little Auster AOP's used in Malaya and the big Sunderlands. Buth low flying so no need for an atmospheric lock mechanism.
LAST used in the UK during the 70's when those left in Ordnance were converted to riot guns to fire rubber bullets and tear gas. The barrels were extended and Sten gun type butts welded on.