Originally Posted by Piwo

You cannot put a model 12 barrel on a model 10 because the barrel shank that protrudes through the frame is too short. This is due to the fact that the cylinder on a model 12 is longer than a model 10. It is the same length as a model 19. The reason for this, supposedly, was that the extra length would help in the case of bullet jump in the lightweight alloy frame.