If one checks early Hunter Arms catalogs, one will find 20 gauge guns regularly offered in weights ranging from 5 1/2 to 7 lbs. Obviously, barrel length and wood density were huge factors in finished gun weight; BUT a gun ordered with the auto-ejector option would obviously be heavier than a manual extractor gun due to the added weight of the ejector mechanism. When a customer specified a certain weight for his gun, Hunter would often bore holes in the butt stock to either add or subtract weight; and or change a balance point. They would also drill lightening holes in the frame beneath the narrow portion of the lock plates, and sometimes in the rear portion of the frame also (a Journal article featured such a frame in an article many years ago); so the answer to your question is that a customer could certainly order his gun as a light weight model. Hunter Arms even offered 12-bores in weights as light as 6 lbs.; and some years ago I was the proud owner of a 1912 vintage Grade 3E with PG stock, FW frame, HOT trigger, and 28" Nitro Steel barrels that weighed 6 lbs. and 8 ounces. It was the best shooting Smith I've ever owned and a gun I wish I'd never traded.
As to "is my gun a Featherweight", this question has nothing to do with the weight of a Smith gun; the term "Featherweight" is only a reference to frame type. Hunter made two style frames, a Regular Frame (offered at commencement of gun production) and a Featherweight frame (introduced in 1907). The most obvious visible frame type differences are seen in the shape of the lock plate and size of the cut for the barrel lug; but the easiest way to make a determination of what frame type one has is via the screws attaching those plates to the frame. A Regular frame lock plate will show only one visible lock plate screw slot; and it will be seen on the left side lock plate. A Featherweight frame will feature two visible screw slots on the left side lock plate and only one screw slot on the right side lock plate. It seems a customer could specify frame type up until about 1940 or so (only the Featherweight frame was available afterwards); but if a customer wanted a light weight gun HE MUST SPECIFY gun weight, as guns with Featherweight frames weighting more than a gun with a Regular style frame are often encountered. I hope this information is helpful.