USMC .22s?

I saw an advert for a brick of Western .22s that the guy said is USMC marked: “Inside flaps of all boxes marked USMC 1942 and lot number”. I don’t have any interest in .22s, but I was curious if that is actually rare and interesting, as the seller states. He wants $500 for the brick. I’m not buying or trying to sell, just wondering if the guy is living in Fantasy Land.