Because LC Smith are normally lighter than the average when it comes to doubles. Physics. Id love to know how much it weighs, likely less than a Fox or Parker or other era double gun. To each his own.
To the OP. Make sure you run the serial number and know exactly when the gun was built, and or have the chambers measured. Smith 20’s had 2 1/2” chambers until 1936, unless it was stamped on the gun 2 3/4”. After 1936, I don’t believe they stamped them with the 2 3/4”. My 1923 Trap Grade has 2 1/2” chambers and my 1942 Field Grade has 2 3/4” Chambers, neither are stamped.