RWTF,
As I understand it, the "extra" carrier shell guide was first used on the 28 gauge gun to keep shells from getting too far off center laterally when being routed to the chamber. The action was wide enough for the 16 gauge, and the small shell needed some containment in some gun attitudes. Next, I understand this extra part went on the 3" guns. Even with this guide I still have feeding problems occasionally with my 3" duck gun in vertical positions when pass-shooting. Finally, sometime post war, they put this part in all Model 12's. That is my understanding, I think this is covered in either Riffle's or Madis's books.
One of my Model 12's is a 20 which my dad gave me for Christmas in 1964, when I was 13. I still have it. For the first two years of its life it ate ejectors regularly -- broke the springs! It could have been catching the ejector on some burr, but I could never find it. The gun was extremely tight when new. More likely the problem was basewad junk blown out of those damnable old paper Federals that I reloaded until their chintzy brass bases burst. This junk probably got between the leaf spring and the ejector somehow. That's how I learned the inside of Model 12's, changing that ejector several times before my 15th birthday! I haven't had to change one in decades.
