The pre "Y" model that I have, has a smoother action than the "Y" model that I had. You may notice that I said "had". I sold the "Y" and kept the pre "Y". The gun that I kept was a 1955 round post donut base trap model. In my opinion it was the better if the two.
I have always been told by model 12 owners that pre 64 model 12's were a better gun than the Y model 12. Reason, they were smoother, and supposedly had no stamped parts. I have had both guns, and the pre 64's were smoother. I knew a very well respected gunsmith in my area who's specialty was in model 12's. He said, although the Y models had stamped parts, in his opinion the Y model was mechanically a better gun. He is the only person that I ever knew that felt this way. All I can say is when I go to a gun show a pre 64 model 12 will usually sell for more money over a Y model. Like I said I have owned both. I would take the pre 64, maybe it's nostalgia.
I have both Y and pre 64 model 12s and have shot thousands of rounds through both and other than a pigeon grade my Y model is a smooth as my pre 64s. If I worked the actions blind folded I couldn't tell one from the other. There both great guns. Tom