Bobby,
Most say Simmons did do work for Winchester as far as adding vent ribs. If the work was done for a factory gun, then the proof marks should be visible, with no "Simmons" marking. If he work was done for a customer after the gun left the factory, then it would be marked as "Simmons Gun Specialties" and part of the proof marks would not be visible. If it is "Simmons" marked, then most likely it was done by a customer who sent it to Simmons to have the rib added.
Addition: Supposedly the Book "The Model 12" by Gorge Midas goes into your question.
I would think it unlikely that Winchester would have a factory shotgun marked with another companies signature.
Last edited by battue; 03/23/23.
