I bought a new 637 just about a year ago. First time out, I found the thumb catch to be "gritty" and on one or two occasions wouldn't release the cylinder. Sent it to SW and they repaired and sent it back in a short while. Repair was listed as "Repaired bolt" and said it was adjusted to their standards Got it back, tried the release, seemed ok, into the safe it went. Should have taken it out and fired it when I got it back but one thing led to another, and it was some time before I got it back to the range. Same thing. Back to Smith, same repairs, "Repaired Bolt", etc. Seems ok now but not anywhere near as smooth as my old Smiths. Or even my new 686+. Keep an eye on it. Good luck.