DD's are a 200 tax there, and as long as it is not an explosive round there would be no registering of the round itself. For instance you can buy an LMT M203 and pay the 200 tax for the registration of a DD, and shoot hand loaded chalk rounds or "Beehive" rounds out of it all day long and you are fine. To get the HX rounds you would have to find someone that would be willing to sell you one which is near impossible, but in order to buy them you have to get an explosives license, meet federal, state and local ordinances to have an explosive magazine and then pay the 200 tax for each round.... Out of the question for the average person.

The only NFA item that is a 5 dollar tax is an AOW, and that is for the transfer, if you make your own AOW and are not a licensed SOT manufacturer you are forking out 200.00.