I agree with the last couple of diagnosi (sp?) When you look down on the lock plate on edge, there should be just enough space between the cock and plate that the cock just passes without rubbing - no more. If that gap is excessive, the square on the hammer can be cut closer to the plate, allowing the cock to be squeezed onto the square just a bit further. Having done that, be sure the square is not too long, preventing the hammer screw from bottoming against the cock.