Take a fired case, one that chambers with difficulty.
Run it through your sizer and decapper die. Do not prime the case. Try chambering the case - is it easy or is it difficult? If difficult, adjust your sizer downwards, until the case freely chambers.
Bell the case (if you do this step). See if the belled case chambers freely or not. If it chambers with some resistance, that not necessarily a bad thing. If there is resistance, then run the case into your seating die (without a bullet), in order to apply whatever roll crimp you have adjusted for. This ought to chamber freely - if not, screw your seating die down in small steps, until you get enough roll crimp to take out the case mouth expansion and have the sized-belled-crimped case chamber freely.
Back up a step, bell the case again. Now seat a bullet (no powder, no primer). Does this bulleted dummy round chamber freely? If not, it is because your bullet is hitting (or perhaps your chamber is dirty), or the bullet is oversized and is swelling the case mouth too much. In the former case you can fix this by adjusting the seater stem to seat the bullet deeper, until it chambers freely. If the bullet is swelling the case too much, you need to find a brass/bullet combination that fits in your chamber.