it sounds to me like maybe you do not have the sizer die screwed all the way in. on my lee dies, you have to screw the die in until it touches the shell holder with the ram all the way up. if there is even a few thousandths of clearance between the shell holder and die bottom, the brass will be sized just a few thousandths to long. that would give you the hard closing/opening you are talking about, as it would be close, and kind of a press fit by the cam action of the bolt.