I too have a Stag 6.8 upper (purchased a month or so ago). I was concerned as well about what chamber they used since it's not listed on the barrel anywhere. I called Stag and spoke to a very helpful tech...he said exactly what paulosantos posted above.
....actually, I had also sent them an email a few days before I tried calling them, and shortly after my phone call they replied to my email inquiry....here is the email I sent them and their response:
I recently purchased (but have not yet received) a Stag 6.8 (5H) upper and am trying to find out for sure what chambering you use for your 6.8 SPC barrels. I know that your website lists it as a 1/10 twist barrel, and SAAMI chamber, but I've heard rumors that your chambers are actually improved SAAMI spec. Is this correct? Please let me know any specifics that you have. I am interested in using some of the Silver State Armory "combat loads" which are a little hotter than normal 6.8 SPC. As I understand it, this should only be done in a rifle with an improved SAAMI spec chamber, and I believe this improved SAAMI spec chamber has improvements made to the lands in the barrel as compared to the original 6.8 SPC SAAMI spec....i.e. where the lands begin with respect to the throat of the chamber and how aggressively they are angled. Again, any insight or additional information you can provide will be greatly appreciated. I have several other Stag rifles, and am looking forward to using my 6.8 SPC!
Thanks,
Reply
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We use the Spec II chamber in our 6.8 rifles and upper halves your Siver State ammo will work fine.
-Sales