Originally Posted by timmyatnop
Has anyone here, ever fire formed 243 brass to 6mm cm cailber. If so have u ever got a donut around the inside of the neck, and if so what is the best way to remove it?
Not that conversion, but I've fireformed plenty of rounds. Usually if you don't get complete fill, you are a bit light on the fireform load. I asume that's what you mean for donut. Simply fire it again with a full pressure load if it's only a small fill issue, and if it's a bigger issue, you need to step your fireforming load a bit.
Reading your other post it seems you also have a thickness issue. You may have to remove metal by turning or reaming the necks then; I've never had a thickness issue and I've done hundreds of rounds to other calibers.