Johann Peterlongo founded the company in 1854 in Innsbruck, Austria and it was in business at least until post-WWII. While the primary business was high quality sporting rifles, there was also a retail operation selling guns by other makers.
FWIW, I think it unlikely that the Peterlongo shop made that revolver; more likely it is Belgian and was retailed by them. The initials are more than likely assembly/inspection marks. If you could find any proof marks, they would narrow down the country of origin of the revolver. The gun certainly does not date to the 1920's; that type of gun was long obsolete by that time.
I can't tell for sure, but it almost looks like a pinfire. Those guns were reasonably well made, but were not high priced, being the equivalent of H&R or IJ in this country. An almost identical one, without engraving, is shown in the 1911 (German) Alfa catalog at 8 marks, or about $2.00 at the time (about $80 today).
Mostly those guns are of interest as novelties and (if pinfire) an example of that ignition system. In good shape, they sell at gun shows in the $100-200 range.
Jim
