So I stand corrected. There is a law against straw purchase of ammunition. But the WalMart associate basically called your buddy a Felon.
Federal law imposes several restrictions on the transfer and possession of firearm ammunition. The law prohibits the possession of ammunition by convicted felons, controlled substance users, and anyone subject to a domestic violence restraining order, among others, and it prohibits transferring ammunition to such persons as well. It prohibits the sale or transfer of (1) long gun ammunition to anyone under age 18 and (2) handgun ammunition to anyone under age 21. It also strictly regulates armor-piercing handgun bullets.