My dies and shell holders are both RCBS. I found when I turnedmy FLS dieout another 1/4 turn I could actually feel a small cam over which tells me even though it looks like they're touching there still could be enough play to not fully FLS the entire case and evidently even a tiny bit of unsized case makes a world of difference especially if your rifle would happen to have a tight chamber. My shell holder did appear to be touching the the FLS die but when I turned the die out 1/4 turn more it instantly fixed the problem and my bolt stopped being stiff to close.