So I was making a routine trip to gander mountain to get some 209 shotgun primers. I get up to the register and they ask my birthday (I'm 18) and they inform me that I not of legal age to purchase these. The part that bewilders me is that I can go back in the store and buy as many boxes of shotshells (with the same primers in them) as I want. Is this a federal law, a state law, or just a gander mountain store policy?