The MilSpec .300 Black Out, also know as 7.62x35 is in the Navy's armories. I was *thinking* that the cartridge laoding, may have been a "Mark" something or other. I have seen the military issued boxes at a Virginia Beach shooting range frequented by SEALs.
So by that definition, it may *not* be MilSpec, if only the SEALS and Delta use it. 300 blk as been in use for years, in limited issue. There have been AAC manufactured suppressors and guns earlier, to SIG Rattlers that were put into inventory more recently. To my limited knowledge, the Army nor Marines have been issued any guns outside of maybe limited testing.
Tom In Va.