It is a very nice gun. I think it would have sold were it a 16 or 20 in as good condition.
The people who are interested in a gun like yours aren't getting any younger, and a 20 would be an easier sell to a guy looking for one to use.

The most useful gauge is the least sought out in old double guns at the moment. I guess, long term, I don't see that changing.

Best,
Ted