I've an rcbs die set for my .223 the very first bullet I seated had a big gouge out of the side of the tip. This was because the seating tip (screwed threaded bar at the top) was seated too low. I had to raise this so it didn't pjoect below the aperture at the top inside the die, and the lower the die body.

Tell me if I'm wrong, but without the corrective measure a bullet marginally off centre, the tip will get trapped by the seating piece and the inside of the die body. Unscrew the top piece completely and have a look down the die body, this should help in understanding the problem, you'll be able to removed the trapped bit of plastic tip also. I'd read articles / threads about dremelling / polishing the part the seats the bullet, but I've found if correctly seated in the die and the due body lowered there is no need.

It would be good if it was this as its simple to sort. As posted, I bought mine new and thought they were someone's returns / second hand ones when I encountered this, thinking I'd have to return them.