To add to Mr. Moody's point, Winchester recognized the Heavy Duck as being a distinct version of the Model 12 and it was marketed as such. It was authorized for production on 2/15/1935 and discontinued in 1963. To further illustrate the differences between the HD and a standard field grade, a 12-gauge field grade with 30" barrels is listed at 7lbs - 5ozs. The HD with 30" barrels is listed at 8lbs - 2 ozs. My uncle has a 32" HD that he used to carry all day for pheasants. He's a big guy. The 2004 Gun Digest has an article devoted to the Heavy Duck Model 12.
