Can I ?

[Boomer]

Blasters would buy from an explosive warehouse not a firearm outlet...if the explosive warehouse runs short, they may buy from a store but highly unlikely. they get a much better price from thier supplier.
Cartridge collectors would not likely buy retail in boxes of 20. Most collectible casings are obsolete and not available retail.

i agree that components are in approved containers at the store but when repacked by a friend,....who knows if they do it right? The shipper is responsible to see it is packed safely and to standards as well as labelled. If a friend is repacking and not labelling it correctly ( buses will not ship guns nor component powders..... Airlines?????)

Its sometimes easier for the blaster to go to a gun store for primers if his supplier doersn't have any on hand. So they cost more. Primers cost $4/100 who cares where they are cheaper if you need them and you have thousands of dollars tied up in the blast tied up in a blast?

How does presenting a firearms license at the point of sale prevent anyone form committing an illegal act once they have the components? I don't follow your logic here. If someone is going to illegally ship something, the point of sale is not the place to stop it. Properly labeled components can be shipped by air provided the aircraft has no passengers on board. You can check the IATA regulations for this.