I also have a 617-6 4"bbl that I bought in December of 2011 brand new. Experienced the same symptoms: cylinder binding, misfires, even tried with several different brands of ammo. Called S&W and sent it back to them. They replaced the firing pin, replaced the strain screws, repaired the frame (?) and repaired the internal lock. Now it shoots like a charm with any kind of ammo.
How soon after owning your 617 did the problems surface? What was S&W's turnaround time for your repairs?