I think some of the above information is outdated. Looking at the changes to ITAR effective 9 Mar 2020, weapons and ammunition commonly available on the civilian market have been removed. Regarding the manufacture of ammunition, as long as you are sticking with metal cased non explosive, non tracer, non flechette, non belted / linked smallarms ammunition you would be exempted from ITAR. At least that’s how I read it.
https://www.federalregister.gov/documents/2020/01/23/2020-00574/international-traffic-in-arms-regulations-us-munitions-list-categories-i-ii-and-iii