If the military has adopted the 6.8 SPC, may it be used, or possibly be allowed at a later date, in Service Rifle matches in an AR15-type configuration?
Probably not, for the same reasons that the M4, SPR, SR25, etc aren't "service rifles." There's been chatter about chambering 6.8 SPC in a match rifle though on different HP boards, but I haven't followed it too closely.
