You must be flaring the snot out of them if the bullet is sliding into the case that easily.
Back the flare off to just enough to get the bullet to sit on top of the case without falling off, it should be little enough you need to look for the flare closely.
Back the seater die body up a couple turns.
Seat a bullet to the correct OAL turning the seating stem only.
Back the seating stem out a half inch.
Screw the crimp die body down half turns at a time until it flattens the bell out. Continue screwing it in 1/8th of a turn at a time until you have a MILD roll crimp. You just want the case mouth turned in against the bullet, any more than that is a mess with plated bullets.
Leaving the correctly crimped round on the ram raise it fully, screw the seating stem down against the bullet firmly with your fingers. Lock both the die body and the seating stem.
Done. Should take care of it for you.