it might also be a late bolt release....the cylnder gains speed and rotates freely too much time, too quickly. Esay to correct with care , thougth just a mistake of half a millimeter and we can spoil the bolt,
if the bolt release takes place just a few degrees before full cock, we can have that problem in old Smiths and Colts and in other old type revolvers. Not in vane, Lefaucheux revolvers included a spring in the axis to slow down the cylinder preventing so over rotation.
http://apk-dl.com/lefaucheux-pinfire-revolver/The problem does not take place in modern double action revolvers as the cylinder never rotates freely...it is pushed in the front of the extractor in Smiths and from behind in Colts, that is why very rarely overotate, even with very strictly timed bolts.
the hand spring also helps to prevent the cilinder from gaining too much speed and should be checked, besides all other possibilities mentioned by experts above.
note: I solved today "an ocássional" over rotation priblem in my Uberti by bending the hand spring to gain tension....as a result it makes the cilinder move a bit more forced an slower....so it is allways on time.