This directly from the ATF website:
Q: Is a license required to engage in the business of selling small arms ammunition?
No. A license is not required for a dealer in ammunition only, but a manufacturer or an importer of ammunition must be licensed.
[18 U.S.C. 922 (a)(1)(B)]
(I would suggest that you clear it also with the business license issuer also.)
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)