It's a good idea to run the new cases over the expander ball to round the mouths out. Also a good idea to trim them all to the trim-to length. Cartridge cases often have slight variations in them, a result of the drawing process, these imperfections result in, among other things, case mouths being out-of square. Trimming produces square mouths and uniform case length.
As long as you're putting them through the press to run them over the expander ball, you might as well full length size them too. You also want to make sure your sized, prepped cases will chamber correctly. Do this by making a small number of dummy rounds and chambering them in the rifle they're to be fired in.
Yeah, you might could get away with skipping a step but as I've found out, usually the hard way, it's far better to use the correct procedure all the time, especialy with a batch of new cases.
Do you own a good bullet puller? 'Cause if you don't, and you make a bunch of ammo that ain't right, you'll be needing one. And, trust me, they are, at best, a PITA to use.
