One of two things: Either the extractor rod unscrewed a little under recoil, and now it is jammed against the front of the extractor rod cutout under the barrel, preventing any movement of the cylinder; or, a few granules of unburned gunpowder became trapped under the extractor star during ejection of the last cylinder of empty cases, and when you reloaded and closed the cylinder, the granules kept the extractor from fully seating into its cutout in the rear face of the cylinder, making the cylinder effectively too long, and it is now binding so severely in the frame's cylinder window that it cannot revolve or be opened.

Note: all the following MUST be done with the weapon pointing in a safe direction; safe enough that if the gun were to accidentally fire, no one would be injured or killed, and property damage would be minimal. NEVER point it at any part of your body during handling, of course.

For the first problem, try using a tiny screwdriver to push the small spring-loaded locking bolt (at the front of the extractor rod) forward, which may release tension on the cylinder enough to get it open using the thumbpiece (if you can see any part of the bevel on the end, try to work the blade in far enough to press on this angled area). If that doesn't work, try pressing inward on the left-rear edge of the cylinder with your left hand, like you are trying to close it into the frame, and at the same time, use your right hand to press the thumbpiece forward to release the cylinder from the frame. If you can get the cylinder to unlock using the thumbpiece, it then should be possible to roll it out and unload it. Alternatively, keep pressing forward on the thumbpiece while alternating between pushing in (closing motion) on the cylinder, and pushing out (opening it) to get it to wiggle free.

Second-to-last resort: If you know how to completely disassemble a S&W revolver, you could remove all the internal frame parts, and then use a soft metal rod or punch to tap the center pin out of the recoil shield to unlock/open the cylinder.

Last resort: take to local gunsmith (transport VERY carefully if still loaded), tell him what happened, and let him take it from there. Be prepared to spend $50 (minimum; likely more, maybe MUCH more) for diagnosis and correction of the problem, and an overall inspection for bent/broken parts once he gets it open.

CMC,
I had a similar thing happen to me a few weeks ago, try pushing the thumb release towards the back of the revolver, while holding the release back try to pull the hammer all the way back, if you can do this, I would say the your bolt is probably broken not allowing the cylinder to release. the bolt is the piece inside the frame that the thumb release attaches to and when pushed forward it is the pin in the frame that releases the cylinder, although DJ Niners answer could laso be the issue, I would try his first, like I said if you push back on the thumb release and you can pull the hammer all the way back it will be the bolt.

Thank you very much for the info. I'll be trying to correct it tomorrow and if I cant then its to the local smith. This was my first endeavor into the revlover spectrum. More a show piece for the collection but had to check functions and I'm blaming operator error of some kind knowing that S&W makes some of the best revolvers around. I'll keep everyone updated how it goes in the next few days.

It was the extractor rod. Thank you very much again for the help.

Glad you got it worked out! 629s are sweet shooters; can't have them sittin' around, not making their share of noise...

Now you'll want to get that cylinder pin screwed in tight and perhaps Lock-tited to avoid a reoccurance. CMC, did you have to resort to a 'smith, or did you get it yourself?

If you choose to remove the ejector rod to Lock-tite it, be advised that the threads are very fine and in some cases left-handed. A buddy shipped me the cylinder from a 586 so it could be reinstalled....Don't recall now if I used Locktite or just put it in the leather jaws of a vise and cranked it good and tight.
Glad you're fixed!
Moon

Halfmoon, i didn't go to the smith was able to resolve it myself. and i would love to lock-tite it but unfortunetly i just moved back into the parents house after getting out of the Corps and they are not gun people so the pistols have been locked up and don't come out except for once a month for a quick function check and then put back. Their house so have to play by their rules for a few more months. but ill make sure to try what you suggested next time i can take them out for more then 5mins. haha.

CMC, we thank you for your service.
Do some checking here as to the 'dash' number of your 29 and whether it has left hand thread; I'm not knowledgeable enough to give you a good answer. In theory, at least, the left-hand thread guns should tighten with use. In any case, once you have that information, you'll want to tighten the ejector rod and see if that solves the problem; if it reoccurs, then you may have to resort to Locktite.

As far as the actual tightening process, you want to either use a vise with soft jaws (leather or lead) or a tool made specifically for the task, available from Brownells.
Moon

I'm pretty sure S&W changed-over all their extractor rod threads to left-hand threading by the mid-60s; the 629 wasn't introduced until the late 70s, so I'm almost certain that it will have a left-hand thread pitch.

Not that it matters much; I've seen both types loosen with use.

Originally Posted by DJ Niner

I'm pretty sure S&W changed-over all their extractor rod threads to left-hand threading by the mid-60s; the 629 wasn't introduced until the late 70s, so I'm almost certain that it will have a left-hand thread pitch.

Not that it matters much; I've seen both types loosen with use.

DJ, that surely sounds right, tho' I seem to recall running into something right-handed more recently than that.
For the OP, try turning the ejector counter clockwise when viewed from the muzzle end and see if it tightens....or not. You may well be able to turn it with your fingers initially, but you will need the tool or soft-jawed vise to snug it up. If you should happen to unscrew it completely (try not to do this...), be careful when retreading; the pitch is very fine and a cross thread entirely doable, especially with the bassackward thread.
Left hand thread just feels so wrong in about anything; do you recall some cars (Chryslers especially) having left-hand thread on the driver's side wheel lugs?
Moon