Strange that you should post this picture and certainly am not an expert but recently acquired a piece similar to this one and it is a Forehand&Wasdsworth. Look along top of the barrel rib and well as the bottom of the butt grip. Mine information was hard to read, does list a S/N but no caliber. I Understand that the configuration of the trigger guard is a Smith design which other copied. Finally figured out that it is a .38-S&W. If you can, pull the grips and see what type of hammer spring, it has. …….
https://www.gunbroker.com/item/849075853
https://www.youtube.com/watch?v=S6zkZQEFU08
Be Safe !!!