Thanks, John. This "thing" is from the well-known "Maryland" Steuart collection of Confederate firearms at the Va Hist Soc (old Battle Abbey collection) and is currently in an exhibit on blockade-running in the entrance area of the VHS. (I see that both as indication of "age" and involvement of serious collector/expert, by way of provenance. Not an eBay find!) Specs contained in accession notes at the link herewith.

Catalogued as "Signal Pistol, Confederate."

Obviously (IMHO) this was not used for setting off/burning a Coston-type cartridge, unless with addition of "sleeve" of other attachment. A collector better acquainted with late 19th/20th C flare guns (Very-type) has likened it to a "fuse-lighter."

As you'll see on the link, it is marked with Broad Arrow and letters "W.D.", a well as the "CS" and name "Carolina"[sic] (perhaps the blockade-runner of that name). Bore of the 2 1/2" barrel is c. .31" and overall length is 8" (20.32 cm.) Has belt-hook/clip on right side

I am pursuing this as side-line of interest in CS signaling, and, knowing something of the employment of army signalmen on blockade runners for IFF/ship-to-shore signaling, thought that this might be an item standard to British registry steamers of the 1860s, if not naval.