here is what the Ruger CEO had to say about it.
Dear Mr. Dearborn,
Please know that the so-called 6.8 SPC II "spec" is not SAAMI approved. To the best of my knowledge, Silver State Armory does not manufacture ammunition to SAAMI pressures and the solution they have come up with is to relive the throat to drop pressure. That is not the correct approach, in my opinion. The 6.8 SPC cartridge and chamber were introduced to SAAMI so firearm AND AMMUNITION manufacturers have a standard to manufacture to and everybody's products work together.
And I don't think your average deer will mind if you use 6.8 SPC.
At such time as SAAMI adopts a new 6.8 specification, we will be glad to look at chambering rifles in that new specification.
Best regards,
Mike Fifer, CEO