Simply open the cylinder, pull back on the thumbpiece and cock the hammer. The tip of the hand should not protrude ahead of the breech face, if it does then the case rims will catch on the hand. Sound familiar?

The second definitive test is to load the cylinder (empty cases, dummies), hold the gun muzzle down and try to cock the hammer. The cases should not catch on the hand. Next hold the gun muzzle up and cock the hammer, now the cases will catch on the hand!

The solution is to trim the point of the hand so it doesn't protrude past the face of the breech. Don't cut it any more than absolutely necessary. Keep the face of the tip square, do not bevel or round the corners!