Eightbore is on the right track about illusions. The length of the frame behind the breech adds a look of length forward of the face. Too, I think the height of the action bars and the degree to which the frame is narrowed across the hinge pin can alter the apparent length. Most of the American-made frames have a similar working length (forward of the breech), and I see that the Smith is of similar length to the M21 and Parker, but the LeFever is longest at about 2.75" I bite my tongue when people ascribe the M21's strength to its long frame.
To Jeff's original question, the M21's side view is really pretty expansive and it's hard to find a better candidate for well planned custom work.
