You can definitely order a black powder pistol (and the caps and balls and powder) through the mail, no background check required (I guess some states do have restrictions, mine apparently did not).
I ordered one years ago and the delivery service left it with my neighbor who's id they did not check.
I ordered one years ago and the delivery service left it with my neighbor who's id they did not check.
http://www.cabelas.com/catalog/product.jsp?productId=735152&...
Granted it's not a sub-machine gun and takes a bit to load but it is a repeating firearm every bit as deadly as one that uses conventional shells.