In new brass I usually run a mandrel through the case mouth or use the expander in a die, to make sure they are not āout of roundā. Then I load them and fire. This will fire form to your chamber (kind of). Then ask Lance what to do next. @lancetkenyon š
In the past I would then full length size with the die touching the shell plate and that was it. I learned with my ultra mag that this works but after a couple firings on the brass, it can be difficult to chamber. I wasnāt bumping the shoulder back like I thought I was.
Get a headspace comparator set. Iāve found it very useful and have eliminated this issue by measuring after firing and then bumping the shoulder back .002.