I don't suspect Antique in the sense of pre-1889.
The frame style suggests otherwise.
The rear sight is German/Austrian style
The breech mechanism is/was a common type used on
Single shot Target pistols ,,Scheiben and Salon Scheiben.
The latter the common 'Shoot for Drinks' indoor bar game of the past century in Europe.
Those Salon Scheiben pistols could be ordered rifled or smooth bore as a rule fom the better makers.
Mostly just called Flobert type pistols now but there are many different styles of actions, breech systems and overall handgun designs.
Here's a link to a J.G Anschutz catalog from 1937.
J. G. Anschutz 1937 Catalog nr. 32 & Net Price List – German Hunting Guns
Not to far into it you will find the pistols mentioned with this particular breech type and extractor.
The grip frame style isn't shown, but the OP's gun could possibly be a small maker or one made much later by a gunsmith.
The coil mainspring and semiauto pistol frame, trigger and round hammer style hint to that.
It looks very well made.
W/o any Proof marks on it, I'd guess it was made 'here' and not in Europe. Someones basement machinest project. The assembly numbers suggest more than one being made but those machinest types are good at keeping things squared away in the 'be neat about it' dept.
The bbl may have been part of the project as well. Made the whole thing,,just didn't have any way to rifle the bore.
Possibly the firing pin is a bit too long and a relief has been made in the rim recess so it doesn't damage the breech face.
Looks like the hammer was dropped a few times with the breech block not quite closed all the way and the FP punched the breech face just to the side of the chamber as a result.
I'd line it to .22rf so it had rifling in it. They frown on smooth bore handguns. Or it would be simple to fit another bbl to the frame and chamber. It's a simple design and any style and length could be easily made.
A set of grips would be an easy make also.
Very neat handgun..
and just what I see looking it over.
...That JG Anshutz catalog is very handy in ID'g German commercial offerings of the period.
