HK - the gunmaker's name, best grade, a date is not sufficient for much of an opinion. Watson's made a wide range of guns, as did most makers (had to to keep the doors open!). A photo(s) would be very useful. Following is tip on three field of information that help understand guns and values.
For Brit and Continental guns, a target value for a 12 bore SxS (1890ish to 1960ish)of typical finish at USA retail can be established from Brand Value level of the maker's name, the Original Quality grade of the individual gun, and Current Condition level. Maker's name is not sufficint information for pricing as most makers made a wide range of guns and guns vary widely as to the condition they are currently in. Watson's has BV level two (BV2). They will price at 2/3 of a BV1 and 1 1/2 times a BV3. If the gun is a best grade from 1926 (the style was well set by that date), it will be a sidelock ejector with near 100% coverage of engraving, excellent metal to metal and metal to wood fit, stocked to the fences, enclosed lumps, probably a H&H Royal type action, excellent barrel striking, wood of very high quality and, likely, "flashy" figure; basically, no compromises in workmanship or materials.
Post back to discuss further and if you have more information.
