Not sure Amigo. To be honest with you Fred, I've never had that screw out of mine. Wonder if he didn't tighten enough, or even over tightened to where the screw threads protruded too far? Glad for the guy it didn't blow his chin off.I wondered the same thing.
Or doubled up the load and or the balls.
Would it do that if he forgot to put the screw back in after cleaning?