FWIW I believe(!) that a license is required to
conduct business in making ammo, but is not necessarily required simply to sell a few handloads now and then. IOW it's similar to selling the occasional gun at your local gun show.
Example:
"Hey buddy, I've noticed that those .308 handloads of yours shoot really well. Can you load 40 rounds for me? I'll give you some money to cover your costs." -
OK
"Can I buy 200 boxes to stock my gun store?" -
NOT OK 
Mandatory Disclaimers:
- I could be wrong about this. If so, someone please edu-ma-cate me- I'm curious, and you won't hurt my feelings.
- I do not intend to suggest that I would personally engage in this type of transaction. I wouldn't, due to my fear that one of my handloads might blow up someone else's pride and joy.
