A good way to set up your crimping/seating die is to use an unflared, resized case.
Note if they hang up on the feed ramp, it tends to mean they are too short. If the loaded rounds seem to not go into full batery, and/or are difficult to extract it tends to mean the flare has not been fully removed. In some cases with cast lead it can mean that they are too long, though that is usualy a rare occourance. More times than not it is that the flare has not been fully removed.
With semiauto brass you are not realy crimping. You are simply removing the flare, and slimming the case back down. If you run your finger nail down the bullet and it does not catch on the case mouth then your round is way over crimped. You should feel a light catch.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.