Just bought a new 617-6, last week ($900). The chain sporting goods store wouldn't let me function the action-- the gunlock remained threaded through the frame until after purchase. When I got home I discovered the cylinder stop would not index-- it simply dropped into the frame and stayed there allowing the cylinder to spin freely with the hammer down, etc.. S&W has provided a prepaid label since the store will not accept returns. It's gone back to the factory. Within the past year my newly-purchased M-66 was returned (barrel replaced) and a new Bodyguard 2.0 suffered magazine follower problems. Three S&W headaches in a year? It's a sad commentary on a once fine gunmaker.
I am thinking that the Cylinder Stop was fit too tightly (or not at all) or is hanging up on a burr. There could also be a broken or bad spring but more likely that the part itself just needs a bit of minor fitting.
While you absolutely did the right thing by sending it back, I would have just fit it or replaced it myself. Having to do that on a brand new gun is pathetic - but it is what it is! It would have not taken very long and I have way more confidence in my own GS skills than the Factory GS's now days. I have commented about the state of affairs with the Company so I won't rehash it here - and I feel sorry that you need to send a brand new revolver back. That is just so wrong and could have easily been avoided if they knew how to do a final QC check before boxing and shipping.
I am a huge S&W fan - but the caveat is nothing they made after the early to mid 1990's. When buying a vintage gun I check it out thoroughly before hand. I have not yet encountered a LGS that won't let you cycle a used revolver or pistol however if I ever do I will explain to them if they won't let me do so, it is a deal breaker. I guess LGS do not like to deepen the cylinder turn line or take a chance of a customer dinging up a new gun. That said, for me, no check out - no buy, even though I know their reasoning for not letting me check it.
There have been a couple of vintage revolvers I did buy that I knew had an issue, but I knew right at that moment what the issue was, had the parts and knowledge to fix it in just a few minutes. Because of those issues I got a fantastically low price as the LGS knew and understood about the issue after I explained it to them. If I did not know
exactly what was wrong, or if I did not have a replacement part or skills to repair it, I would have passed. Of course the agreed price must be in line with the revolver as well.
I guess we all now know just what a great reputation S&W has had for so many years - as they have been solely riding on their past reputation for a few decades now. They have successfully hoodwinked so many new buyers over the last 20 years but I truly believe their "new" reputation is starting to catch up with them now - big time! While this is so sad to live through, it keeps raising the selling prices of high quality vintage guns.
Hopefully they will fix your problem fast, correctly and return the gun to you quickly. Keep us posted and good luck.