Either way, not a good idea to run a completed cartridge into a sizing die. Even with the decapping pin removed, you are squishing the bullet diameter.
What he meant to say was he ran a loaded round back through his CRIMPING DIE. Don’t let them give you a hard time!! “Being new at anything Su***! It is PERFECTLY SAFE!!
A resizing die shapes the outside as well as the inside. In order to correct case mouth it goes down inside the case mouth as well. If you run a charged cartridge with a projectile in it, it will push the projectile down into the case.
You possible break the die. Push the projectile to far down where you can't get it out. I would avoid that at all costs. That's if I am reading your post right. If not disregard this post. Also the one before it.