A lot to digest in this thread, and a lot of great info. Its interesting to have a gun that is somewhat baffling to even the most experienced collectors / historians.
If the gun IS S&W, why SA and why 41 Colt? If the gun is NOT S&W, wow does it appear well made.
Here is my question which really hasn't been discussed yet:
We have a gun that "41 long colt fits inside" without wiggle ? We have to assume the OP would also try a 44 S&W or the like to verify its at least 41 cal but smaller than 44. Given that, how do we explain why it was made in the caliber 41 colt (assuming that IS the cal) if in fact a S&W prototype? We have to assume the idea was to possibly make a larger number in the same caliber.
If you look at US sidearm development, in 1889 Colt churns out one of the first successful DA cartridge revolvers which was adopted by the US military (army and navy IIRC). Why would S&W make a revolver SA, which has traits in common with circa late 1890s S&Ws, when Colt already had a DA? Why would the US army or any other military consider a SA when the DA exists? Also, why the 41 colt? 45 cal was a proven man stopper and was well thought of, and later on we find out that the 38 colt was a little too weak for a military sidearm. The solution was then logically to marry the 45 (in this case 45 Colt) stopping power to a DA design, not a SA, hence the Colt 1909 army revolver. If the idea was the to split the difference, the prototype, if made by S&W, should have been an early DA IMO NOT a more primitive revolver type. In addition, as Lee said, why would they make this "prototype" when logically, it was made either right with a 1896 prototype, or perhaps made after the 1896 production began?
Also, in S&Ws history, you have S&W famously refuse to make any revolvers in 45 colt which the Army considered to be the best of both worlds, in most respects. Take the better design for military use (schofield or a model 3 derivatives) with the better cal, 45 colt. Why would S&W make anything in 41 colt AFTER that? Also, the 41 colt was never really that successful or well thought of (compared to 45 colt) for S&W to bother even making one prototype in that cal. The same is true if the intention was commercial. Its an older design coupled with a lack luster cartridge - what is the motive? I can't think of one.
Now of course, I am only saying this IF the gun is in fact 41 colt. It could be a cal that is close in width and length, but I don't know of any other one off the top of my head. A key to this puzzle is to 100% positively identify the cal, if it can be done.
Speculation- prototype for army review pre-WW1.
There is little reason this is possible for many reasons in this thread and my post regarding the cal, if 41 colt.