I just had to get a sb body die for a new ar10. Most of my brass has been through a hk91 at one point or two or three, and they would not chamber in the tight ar10. Never had a problem with 223, but a combination of the right (wrong) chambers will require it occasionally. If you have only one chamber to feed, and set up your FL die properly (or NS for that matter), there should be no need for a sb die. I did have to body die a 300 win mag but the belt makes that a slightly different situation.
I have run all sorts of primers in gas guns and never had a problem.