That is not a 617-4. It has the lock, it's a -5
A -5 is 6-shot. I meant to say 617-6.
The 617-2 had a 10-shot aluminum alloy cylinder; All of the others have stainless steel cylinders. Some of the last 617-2s apparently had stainless steel cylinders. The finish on the 617-2 is bead-blasted to match the clear anodized cylinder.
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