[Jack]

The way I heard the S & W Model 19 story is this: S &W was designing that revolver primarily for the police market. At the time the Model 19 was introduced, the standard routine in most PD's was for the officers to carry 357 duty ammo, but practice with 38 wadcutters or other 38 loads- much less powerful than 357 loads.
Under those conditions, when the 19 had lots of low pressure 38's fired in it, and few 357 magnum loads, the revolver did fine, and had the benefits of being lighter than the N frame, and having a smaller grip for small handed users.
So, everyone was happy.
Until police departments began to do more realistic practice, using the ammo they actually carried in the field- 357 magnum. Then those forcing cone cracks began to appear. Smith introduced the L frame to solve the problem- slightly beefed up over the Model 19's K frame, but not as big and heavy as the N frame of the Model 27 , 28, 29, etc. The first L frames had 3 digit model numbers (as I recall 686 was one) and underlug barrels.
That's the story that was floating around when the L frame was introduced, as best I can recall it. How much is truth and how much is fiction, I really don't know.