In my tests, the Sherman crews never fire their .50cal when buttoned,the M18 always fire their .50cal when buttoned.It might be open top vs enclosed top thing, I don't know.But from what I have seen "Rambo "is clearly the machinegunner in the Hellcats, for he has no regard for his own life, even when enemy soldiers are close by he always mans the .50cal and always dies and is immediately replaced by someone who dies. Also in my tests, I cant get the .50cal on Sherman76s or Stewarts(.30cal) to fire at all.The Sherman76 .50cal is on the left side in front of the left hatch and no one ever pops up there when you tell the crew to open up.