It's not just loading ammunition, it affects all ammunition components. It includes the cartridge cases, primers, bullets or propellant powder for use in any firearm other than an antique firearm. But you would require a manufacturer of ammunition license, FFL type 06 to manufacture bullets for sale and the same applies to loading ammunition for sale, barter, etc.
The "rub" also concerns the "antique firearm". In discussions with ATF&E about whether the current exemption that applies to "antique firearms" that use metallic cartridge "fixed" ammunition but that is obsolete and not currently available from commercial dealers, as the number of new dealers in center-fire ammunition for Spencers and other similar rifles increases, ATF&E plans to develop new rules to apply to center-fire conversions of antique firearms by removing the current exemption, rendering them as "modern firearms" because they use modern, commercially available ammunition.