All great advice. The only advice I can add is how to find the culprit. First, make sure your FL die is set upas described above. Lube a piece of brass and don't forget the inside of the neck. Run it through the sizing die. Wipe off any excess lube. See if this empty brass will chamber. If it does great, if it doesn't then your die may still need to be adjusted. Once you get a plain piece of brass to chamber then set your seating die as described above. Seat a bullet, no primerno powder. Make sure the COL is correct. See if the round chambers, if it does great, if not your seating die or COL needs adjusting. After you get a round/bullet to chamber then load em up.