Here's some further info on the 686:
686 (1980): Begin production
686-1 (1986): radius stud package; floating hand
686-2 (1987): change hammer nose, bushing, & associated parts
686-3 (1988): new yoke retention system
686-4 (1993): change rear sight leaf, drill and tap frame for scope mount, change extractor, introduce Hogue grips
1995: introduction of 7 shot + model with 6" barrel
1996: deletion of square butt frame; begin shipping in blue plastic case
1997: change thumbpiece; ship with Master trigger lock
686-5 (1997): change frame design to eliminate cylinder stop stud; eliminate serrated tangs; change to MIM hammer, with floating firing pin: change to MIM trigger; change internal lockwork
686-6 (2001): introduce internal hammer and trigger key lock
686-7 (2002): introduce Performance Center variation in .38 Super
Based on this info, If I were in the market for a 686, I'd look for a -4 or earlier model.
This info came from my Standard Catalog of Smith & Wesson 3rd Edition book, which is very helpful.
