The cylinder not opening and closing smoothly on a K frame can be many things . In desending order ill give you the run down from most possible to least possible.
1. Loose Extractor rod ( tighten up extractor rod with some spent rounds in the charge holds . ( Reverse Threads
2. Worn Bolt the bolt that pushes on the extractor rod tip in the frame is worn. fix is replace the bolt .
3. Dirt under the extractor star
4. Ammunition rubs on frame and primer flow..
5. Worn locking bolt getting sloppy and rocking in the bolt cut.
6. Loose thumb piece nut on the sidd plate.
7. Bent extractor rod.
8. worn yoke screw getting sloppy or to tight
9. Worn yoke button
10, Short or worn center pin
11, Yoke out of alignment ( gun dropped or cylinder slammed shut. ? )
12, End Shake of cylinder yoke. more than .005 deviation
13, Worn recoil plate / firing pin bushing backing out into cylinder area dragging on the rounds or cylinder
i have to assume that this is a problem with the gun unloaded as well as loaded. That is why I put the ammo problems also. . Good luck hope it works out for you.