By build it, Started with a box of old Israeli parts (minus the right side plate).
I had to mill a new and highly modified right side plate (which is considered "the gun" by the ATF) All the internals had to be machined to mate with the new side plate. Had to make a new trigger with a disconnector so it would reset after every shot, plus a new sear. Then rivet the whole thing together and refinish it.
It's a little more involved than this, but if you want the details, go here:
http://1919a4.com/
As for the minigun in your pic, I happen to know a few people that actually have built dealer samples. Look in the bulletfest pics.
http://www.bulletfest.net/pics.asp
I personally can't build one of those because it would be full auto and require a class 2 FFL. To get a Class 2 SOT status, you need a manufacturer FFL, which includes Type 7, 10 - and pay a yearly $1000 or $500 (reduced rate for small manufacturers) tax due every July 1st. (condensed version) 😉
