I will try,
to help you understand.
Model 19 and or 66, definitive term "Combat Magnum". A six
shot revolver available with barrel length's of 2.5", 4" or 6".
Model 19's were offered in standard, blued or nickel finish.
The model 66 is the 19's stainless steel counterpart. The
19 and/or 66 is chambered for .357 magnum; but will also
accomodate the use of all forms of .38 Special ammunition.
The model 19/66 is built on Smith & Wesson's K-frame.
The model 586, and or 686, definitive term "Distinguished
Combat Magnum". A six shot revolver available with barrel
length's's of 2.5", 4", 6" or 8-3/8"*. The same holds true for
the model 586, as its offered in standard, blued or nickel
finish. The 686 is the 586's stainless steel counterpart.
The 586/686 is also chambered for the .357 magnum; but
will also accomodate the use of all forms of .38 Special
ammunition. The 586/686 is heavier than it's 19/66
counterpart; and the 586/686 incorporates a fully lugged
barrel, some say to aid accuracy. The 586/686 is known
as the L-frame. The 686+ is a L-frame seven shot model.
Both the 19/66 and the 586/686 have "micro click" fully
adjustable rear sight's. Most of the older 4" and 6" model
19/66's and the 586/686's will come in the form of a square
butt configuration. The newer version 686's will be found
with the round butt. All 2.5" barrel models will be a round
butt style. Prices vary according to model, barrel length,
and locale! Hope this helps some?
Best Wishes,
Ala Dan, N.R.A. Life Member