Well, every one who posted may very well be right, I will add I have used both new unprimed brass and new primed brass, loaded it right out of the box. never had any problem with the bullet falling through or any of it being under sized or over sized. Just my experience. I did this when i was starting out and did not have a supply of brass on hand and I would not hesitate to do so again. Again just my experience.
When you get a new box of bullets do you mike each one to insure that they are the right size and not under or over sized?