That covers that in a nutshell...Only if you manufacture the ammo... Just selling factory ammo doesn't require a FFL. Some states may have more restrictive laws than mine.
Is a license required to engage in the business of selling small arms ammunition? | Bureau of Alcohol, Tobacco, Firearms and Explosives
No. A license is not required for a dealer in ammunition only. However a license is required to manufacture or import ammunition. [18 U.S.C. 922 (a)(1)(B); 27 CFR 478.41]]www.atf.gov