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SGW ! !
As Drew mentioned, it was made about 100years ago - which means that even in excellent condition, it shouldn't be used with any modern ammo, save specialty/lo-pressure shotshells from the likes of RST, Kent, etc.
Ammo companies upgraded shotgun cartridges in 1926, which forced many gun companies to either discontinue or upgrade their shotguns.
Most companies either introduced the upgrades as new models, or went out of business due to the lack of capital for upgrades.
N.R.Davis & Son was located in Connecticut, and went through several different mergers (Davis-Warner, Crescent-Davis) one of the many small companies making guns in the late 1800's to the early 1900's that were eventually bought out by Crescent Firearms, also of CT, in the early 1900's.
AFAIK, the "Davis" portion of the name ceased being used, eventually becoming the Crescent Firearms Co.
Nathan R. Davis started making firearms before the US Civil War, in 1853 - introducing SxS hammerless boxlock shotguns like yours in 1900.
Your gun was likely made between 1890 (due to the low SN) and 1917, after which the Davis-Warner logo would have been put on it.
Today, replacement parts being made of un-obtainium, repairs would have to consist of re-building existing parts or making new parts from scratch - a money pit, in any event.
IMO, the best thing you can do is to protect any innocent folks trying to shoot it in the future by filling the insides of the action with epoxy.
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