The simplest answer to your question, Lloyd, is to simply call your local BATF office and ask. I find them more than happy to answer such questions.
Do they provide documentation that shippers will honor?
That depends. In one case recently, of selling a pistol f2f with an out of state ex-FBI agent, I simply arranged to have BATF speak to him directly on my phone. End of the BS right there. Shippers do not have to ship it. BATF will tell you if the CAN ship it. For example, UPS Stores will not ship guns. But UPS hubs will. It's a company thing.
I have been shipping primers without a problem. I'm comfortable that I'm legal. I have not shipped powder.
I would just call BATF for starters. I doubt you will have a problem with FedEx or UPS hubs if you know the law. But again, company policy may vary.