I have a 15-4, square butt that shoots really great, but it is the most uncomfortable thing to shoot that I own. I dislike how the grip is real small to start with, and then it is real fat at the square end. It just doesn't fit.
I have seen photos of older guns with some kind of "filler piece" that turns the skinny part of the grip into something a man can hold onto. Are these "fillers" still made? Is there a different grip that fits the square butt K frame?