I'd say your FL die is oversizing the brass creating a excessive head clearance issue, not a headspace issue. When FL sizing the brass can't move back(shellholder) or out (die walls) so it moves forward lengthening a case and the more the body is sized the more a case lengthens.
I'll bet if you back off the die then size a case an 1/8" at a time you can watch it grow like a Chia Pet. You have two choices, trim to length after FL sizing or have that or another die honed to minimum resize your brass.
Bill
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