BC, you just apply light pressure with your finger against the cylinder when you cock it so that momentum won't keep the cylinder rotating. If it is out of time the cylinder stop won't pop into its recess on the cylinder.

If it is only slightly out of time it isn't going to cause any problems. It the bullets are impacting the side fo the barrel then you should be seeing evidence of lead splattering or an excessive ammount of copper build up where the bullet is impacting.

If the one cylinder is definetly larger than the others then this is most likely your problem. No real way to fix it that I know of other than purchasing a new cylinder. You can't make them smaller.