I guess they may have saved some money by downgrading the receivers used for shotguns. I just seems to make more sense, TO ME, to just use the stronger receiver for everything and then only have ONE.
Maybe that limited logic is why I still have a job where my name is printed on my shirt. LOL Just don't know.
The folks at Walker Arms in Selma, AL told me that the pre-Marlin models used the same receiver for both rifle and shotguns. Walker is the company that CS referred my to for questions on my 1983 Model 99.