Found this for you. I can't vouch for it's accuracy.....
"no-dash gun should be a 6 shot with the S&W wood finger groove grips and a "no-lock" gun. At some point S&W tried using an aluminum cylinder on the 617's. I think it was a -2 or somewhere in there. They then went back to using a stainless steel cylinder. I think this was on the 10-shot models. Sometime after that they were into the "safety lock" on the guns produced.
617-0: flash-chromed forged parts, non-drilled&tapped frame, 6-shot stainless cylinder
617-1: color case hardened forged parts, drilled&tapped frame, 6-shot stainless cylinder
617-2: CCH forged parts, D&Ted frame, 10-shot aluminum alloy cylinder (transitional, later ones started to have MIM triggers and stainless cylinders)
617-3: MIM hammer/trigger, D&Ted frame, change to integral frame lug, 6-shot stainless cylinder
617-4: 10-shot stainless cylinder
617-5: 6-shot stainless cylinder, internal lock system
617-6: (current production) 10-shot stainless cylinder, ILS"
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