Welcome to the Forum. You have the most popular, most produced S&W revolver. Probably 5,000,000 to 7,000,000 of them made since 1898 and still in production. M&P's from that era typically have very nice actions and a 5 inch barrel should be a great shooter. Safe with any current commercially produced .38 Special ammo, either standard pressure, Plus-P or light "mid-range" target wadcutters. It's built on what S&W refers to as their K frame, and yours is a square butt, if you decide to shop for a holster of different grips.
Looks like Gramps took good care of it. It's a great gun to have.