Most seating dies will also crimp if the die is adjusted lower. Before the bullet is completely seated, the die is trying to crimp, and the crimp is trying to dig into the bullet jacket before it is seated to the correct depth. Crimp dies are inexpensive and you will get a much nicer loaded round by seating first and then crimping in a separate stage, whether it be roll, taper or full profile crimp.
Why do you recommend to seat the bullet and then crimp in a separate stage?
Sierra Bullets > FAQs > Why do you recommend to seat the bullet and then crimp in a separate stage?