Does it happen on each and every chamber? If so, it is likely a problem with either the "hand" that rotates the cylinder and/or the bolt stop. IF it only happens on some of the cylinders, then you probably have a more difficult to fix problem.
You can check to see if the cylinder is over rotating by pushing (rotating) it even fruther clockwise, conversely, if attempts to rotate even further clockwise decrease, even remove, the little "cresent moon(s)" then the hand is not rotating it enough.
I have seen several cheap C&Bs, with their soft metal, that had badly buggered "hands" that were result of shooter trying to use hammer to rotate a badly crudded (from way too much BP powder fouling) cylinder. Result was a cylinder that would not be rotated fully against the bolt stop. Remedy in that case is often a new hand.
It the cylinder is overrotating, fitting a new bolt (cylinder stop) is the likely remedy.
Lars