I'm fairly certain that this isn't a Smith & Wesson. It may be chambered in one of the common Smith & Wesson calibers, but it's likely made by one of S&W's competitors like Iver Johnson, Harrington & Richardson, or the like.

The finish looks to be completely worn off (was some sort of wire brush taken to it?) and I see a lot of empty screw and pin holes, so I'm thinking that this is a parts gun at best. Since it came to you from family you may just want to keep it as is as a heirloom.

Mike