Here is John's expert description of the complex motion of the breech block:
Operation of the breech: The small breechblock is pivoted on operating shaft below it. It can only flip from the vertical (closed) down to nearly horizontal (fully open.)
The huge "wedge" is splined to the back of the small block so always rotates with it. However when the small block and wedge reach fully vertical position (the limit of their rotation,) the "L" shaped cam underneath forces the wedge to rise straight up about 2 inches, sliding in grooves on the back of the small block. This last movement causes the wedge to mate against various forward-facing surfaces on the breechring.
The cartridge extractor operates via the large external wedge cams , and operates much as any firearm cartridge extractor does except it pivots on the shaft over the breech.
The little knob-like control or indicator visible in the picture on the right bears the labels "Firing by lever," "Dismounting of Mech./Drill Stop." The gun could be set to fire automatically upon the loading of a fresh shell.
A firing lever hangs below, for use when the gun was to be loaded, but not immediately fired. It has a hole for a lanyard so the gunner could stand away from the gun. Almost all of the bolts have a 1/2" hole in their heads. It looks as if the gunner were expected to disassemble or adjust the gun using only a "spike". To the left of the breech there is a square bronze piece with a broken end. This was probably a "shoulder stock," as you can see in this photo of a working gun at the U.S.S. Olympia museum in Philadelphia. Their gun is described in a virtual tour of the ship. Although they look similar, the Olympia's gun is not an original Nordenfelt design and differs quite a bit from our gun.
The gun ... is of Italian origin, made by "Stabilimento Armstrong-Pozzuoli", an Italian ordnance company in which the British armament manufacturer W.G.Armstrong-Whitworth held a share and used its patents and designs. At the time of the Spanish-American War some Spanish warships were constructed or armed in Italian shipyards.
A closer examination of the photographs of this gun show a detail of what appears to be the rear sight, which can be moved along a scale calibrated in "MILLAS" (it means nautical miles or knots), with the text "VELOCIDAD DEL ENEMIGO" (speed of the foe).
The breech mechanism is totally different than that of the Nordenfelt. The markings read "Stabilimento Armstrong", "POZLUXXII" (????), No. 458, 57H, 1880. It sits on the Capital grounds, next to the statue of Worth Bagley (the "first to fall" in the Spanish-American War. Ironically, his brother Lt. Cmdr. David Bagley commanded the first US ship sunk in WWI, the Jacob Jones.).
Yet another naval gun in Raleigh sits in front of what was Josephus Daniels' home. As Secretary of the Navy from 1913-1921, he was able to procure this weapon as a lawn ornament. It bears the inscription "Friedr. Krupp, Essen 1891", and is about 3.5" in caliber. Amazingly, this gun's breech is a completely different design than either of the other two guns. This weapon seems to have a hole in the breech block, the block being rotated to close the breech. That is, the breech block is cylindrical, but PERPENDICULAR to the barrel, with a hole through to the bore.
It is almost certainly a German (made) 8.8 cm L/30 quick-firing gun mounted on a central pivot model C/89:
The breech is of a so-called spherical wedge type (Rundkeilverschluss in German). The wedge that closes the breech is actuated using the two-spoke lever to the right of the gun and some sort of short acme screw. When open, the breech block would move to the right bringing the round opening behind the barrel through which the cartridge can be loaded. Missing is the seat for the training number.
This type of gun on this mounting was used as light/medium armament against torpedo boats on destroyers, cruisers, battle ships etc. It was also the main armament of larger torpedo boats.
More details can be found in this book produced by the Naval Office of the Imperial German Navy:
REICHS-MARINE-AMT (1898): Die Schnelllade-Kanonen der Schiffs-Artillerie (für Einheitspatronen) und ihre Munition.- 273 p., Berlin (E.S. Mittler und Sohn). (the two enclosed pictures are from the book)Some more generic reading on QF guns in English: GARBETT, H. (1897): Naval Gunnery.- 360 S., Wakefield (reprint 1971, SR Publishers Ltd.).
- " - (1895): Exercirreglement für die Marine-Artillerie, Nr. XXXIV. Für die 8,8 cm Schnellade-Kanone L/30 in Mittel-Pivot-Lafette C/89.- Berlin (E.S. Mittler und Sohn). (these are the instructions for training with the gun)
Another source of information on WWI-WWII hardware is the Imperial War Museum and the Museum of Artillery in the Rotunda Woolwich, both in London, and, of course, the National Maritime Museum in Greenwich.