Well, this subject is back. John Farnam did an article on this in Feb of 2012.
“When the revolver fires, remaining cartridges in the cylinder (yet to be fired) are subjected to significant G-forces as the pistol recoils. Sometimes, it is enough to persuade a yet-unfired bullet to migrate forward far enough to protrude from the front of the cylinder, preventing the cylinder from rotating normally, and thus preventing the revolver from firing.
He just referred to it again in his Quips from Apr 4th.
During an exercise, shooting factory 115gr hardball from a well-known and reputable manufacturer, a bullet jumped forward far enough to protrude from the face of the cylinder and thus prevent the cylinder from rotating normally. In fact, the bullet jumped forward far enough to physically separate from the case. This not only precluded the revolver from continuing to fire, but it also made it impossible to swing-out the cylinder, so the revolver could now not be reloaded!
Check it out here.