With any luck, Mike or another of the Smith gurus will drop in with proper description of I,J,K,L,M and N frames. Basic ol farts cataloging of em is M early hand ejector, mid sized. I quite small hand ejector with flat hammer spring. J quite small hand ejector with coil hammer spring. K is the classic millitary and police. N is their largest frame. L is intermediate tween K and N.
M very old, I early 20th century, others still in production in assorted forms.
All corrections welcome.
Sam....May the model 19s last forever, and they probably will.