Hi guys just going to throw out a general question here. How old is the .300 Black Out Cartridge?? I was at Cal Ranch today looking at AR-15's one of them there was chambered in 300 Black Out. The gun counter sales guy I have known him a few years told me yea they claim the .300 Black Out was used in the Vietnam War but when he said that he rolled his eyes so I knew he was kidding. I replied I thought it was out just a few years. My thoughts were 5-10 years. But thats my question!