Flint lock by unknown maker S et S
 

Not S & S but S et S. Ought to be French, one might think. But I cannot find a single S et S in Stöckel. S and S is plentiful - in fact, too many to make a plausible identification. Anyway, it was surely not common for British/American gunsmiths to "Frenchify" their company names, although it did sometimes occur with German makers - e.g. the model train makers Märklin Bros. appearing as "Gebrüder Märklin & Cie." (Cie. as abbreviation for Compagnie). And as soon as I try German options, I end up with Sauer & Sohn in Suhl - surely a bit too early for them?

(S&S lock outside-REDUCED)

The lock does not have a bridle for the frizzen/hammer. Which suggests early 18. C. So the French-style ring cock is probably a replacement. The overall length is 14.5 cm, which looks like a small rifle/large pistol size. And it has a fly - just visible in the photo of the inside.

(S&S lock inside REDUCED)

My guess is that it's for a hunting or target rifle.

But who was S et S ???

P.S. Software says my photos are too large to upload. Will reduce resolution and retry

PPS OK photos reduced and uploaded.

This lock- the cock is as already stated a wrong replacement and should be a swanneck cock - is probably or eventually made by the Suhl gunmakers S et S, what I think could stand for Spangenberg & Spangenberg (Johann Gottfried 1722-1795 & Johann Wilhelm 1727-1783). The shape of the lockplate is typical for the first Prussian ordnance rifles introduced in 1744 made at Potsdam and as shows the lock in question perhaps at Suhl too.

Spangenberg et Spangenberg ?
 

Thanks Corrado for a very interesting suggestion. My photo wasn't very good, as one can't see that the pan is also facetted.

I find dozens of Spangenbergs (or should that be Spangeberge?) in Stöckel, but no mention of a Spangenberg & Spangenberg. Can you give me a source for that?

The resemblance to the lock on the Prussian "Jägerbüchse" is striking. And I posed the S et S question some time ago on a French forum, with zero suggestions in response, so it does indeed look as if this is a case of a German firm using a fashionable "upmarket" French style of naming.

This "Spangenberg & Spangenberg" was nothing than a theory, you cannot find this combination in the New Stoeckel. I just looked for two Suhl gunmakers which could have been working together during the same time :)