Well, the Model 33 was originally the Regulation Police, which was made on the old I frame and then, as the Model 33, on the improved I frame and J frame. Both I frame types were the same size as the J frame except shorter, so it would have not been significantly smaller than a J frame gun. The I frame was first used for .32, in six shots; with .38 in the same size cylinder it could hold only five shots.
Jim