Government employees aren't typically Rhodes scholars. Postal employees and the BMV in particular seem to have a high percentage of argumentative twits. I have bought brass from multiple sources (Midway, Dillon, Powder Valley, etc.) There is never an issue with shipping/receiving unprimed brass. Primers, gunpowder, or ammunition is a completely different game. Hazmat fees, must be signed for by an adult, carrier stipulations, etc.

I assume (yeah I know) that your friendly local postal employee is the typical liberal dumbass that: A.) Doesn't think you should be allowed to own guns, ammo, brass. B.) Thinks that the "ammunition shipping rules" apply to empty, unprimed brass (he's wrong) and C.) Isn't the least bit interested in helping you.

Box it. Ship it. If you are asked whats in the box when you take it to the post office, Do Not Lie. Tell them its a box of "thin-wall tubular brass extrusions"