you could do it using a full length bushing die from redding...with no bushing in. I would probably bite the bullet(pun intended) and pull the 300 rounds down, resize with a FL bushing die(decapping rod removed), and reload.It is different, with the bullet installed…..I do not know if there is enough lube in the universe to prevent the case from being stuck in a rifle sizing die with a bullet installed.
maybe I am still misunderstanding something here.