The 686 was introduced in the 1980 as the S&W Model 686 Distinguished Combat Magnum Stainless. It featured flash-chromed, forged hammer and trigger, and had a 6-shot cylinder.
-1 (1986): radius stud package, introduction of the floating hand.
The "M" recall (1987) for the no-dash and -1 guns was to fit a new hammer nose and firing pin bushing to deal with certain brands of ammo causing (potentially fatal) binding when fired.
-2 (1987) incorporated the "M" recall features as standard production.
-3 (1988) floating hand deleted, new yoke retention system
-4 (1993, apparently the most desirable) included a drilled-and-tapped frame, the introduction of the "+" model with 7 shots, flash-chromed hammer/trigger deleted (case-hardened only), new extractor, start shipping with round-butt frame only (no square-butt)
-5 (1997) change to MIM hammer and trigger and frame-mounted firing pin, as well as the frame lug being machined as part of the frame (prior to this it was a separate part, fitted to and pressed into the frame).
-6 (2001, current production) has The Lock
-7 (2002, Performance Center) chambers .38 Super instead of .357 Magnum
Edit: updated with information from the magic book.
