That little cylinder in the bullet seating die, that rattles when the die is shaken, is the actual bullet seater.
The top part that screws in and out of the die just adjusts the seater for overall cartridge length.
The flat end goes up and the concave end goes down in the die.
Walt Kelly, alias Pogo, sez:
“Don't take life so serious, son, it ain't nohow permanent.”