It would be in a 223 Wylde chamber. I also like fireformed and only neck sized brass instead of doing full length sizing. I like the wylde chamber cuz with factory ammo your still good to go but to hit 2900 FPS with 88 eldm would be some sweet performance in a 223!
That's about the only time I would think of a Wylde chamber vs a .223 or .223 AI is if I was planning to neck size only. If you're planning on fireforming though you might as well just go AI.