You are going from an autoloader to a bolt action with the brass? Use a small base sizing die.
If the chamber in your bolt action is tight and the autoloader is looser, you might be running into a situation where you aren't getting enough shoulder contact. You set your FL die with your headspace guage and find that your first piece of resized brass chambers in the bolt action just fine, so you continue.The first piece of brass may have been minimally expanded in the rifle chamber and you didn't set the shoulder back at all with the resizing die. The next piece of brass was still expanding when it was ejected from the rifle, you resize it and end up squeezing the brass down and blowing the shoulder forward. Not having the die set far enough down, the shoulder makes contact with the die but either isn't sized enough or springs back a thou or so which makes in not chamber in the bolt gun.
When setting up your resizing die, measure 20 or so pieces of brass, and pick the ones with the longest shoulders for setting up your die.
If you already have the dies screwed al the way down and 'cammed over' and the brass doesn't chamber, you need a small base die.
Don't, don't, don't screw down the sizing die so that it cams over as written in the directions unless you really have to- its the wrong way to do it.