Phil, in Canada, some Hotchkiss 3 pounders were ultimately used as saluting guns. I came across their history here:
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The text was a screen grab from this site:
http://wwiimodeller.co.nz/tag/photo-wal ... -mounting/Drawings of the breech block mechanisms at a high level of detail are problematical. I have been using patent drawings for breech block details but the end product in 3D CAD is, necessarily, a composite taken from several Hotchkiss patents and from an old textbook that seems to feature redrawn patent illustrations. In any event, patent drawings are not dimensioned and rarely represent in full a manufactured product. It would probably take a trip to the national archives to get truly scale drawings to work from. There were several different quick firing guns that might have been repurposed, I suppose, as saluting guns. In the US these were chiefly manufactured by Driggs Schroeder. Driggs was the inventor, and the patents (and drawings) were in his name.
I have been sketching the Hotchkiss mechanisms mainly as an effort to figure out how they worked. Many of the details will not show in the finished 3D model.
However, I was pleased to see that even with the breech block up, closed and locked, some mechanical detail still "reads".
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When the breech block is dropped, more detail appears.
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In my early 6-pdr, which had no recoil system, the view of the breech block details and mechanism should remain fairly open. Michael
Edit. Ran an image search on US 40mm saluting guns. They are purpose built although some are mounted on crinoline mounts which antedate WWII and are apparently left over from the QF era. In these instances it seems plausible an old QF was directly replaced with a new 40 mm saluting gun.
There are also some YouTube videos of 40mm saluting guns performing a 21 gun salute. These show one sailor loading and a second operating a double lever/crank. The crank seems to accomplish the whole sequence -- I don't see a trigger. The image search turned up a close up of a breech, snapped in a public park, but the block and mechanisms are missing.