The Chamber is .223 Wylde
Its basically a half-way point between SAAMI and NATO chambers
More accurate than NATO, but better suited to heat than SAAMI.
Granted Im not an expert on the subject; somebody more knowledgeable please correct or confirm me if you can :)
This is the Barrel I plan to go with for my AR, but I wont be ordering it for a few months.. Hope you guys are still carrying these in January