For the older crowd who don't watch video, the AK and a lot of other traditional firearms literally force the barrel into the receiver under pressure, while simultaneously gauging the chamber length for head space. It's definitely technical and involves some equipment that isn't part of the norm for most home garages. The basic issue is that the locking lugs for the bolt are in the receiver but the chamber is part of the barrel, and the overall length has to be precisely set.
In barrel extension designs like the M-16, the head space is set by screwing the extension on - by hand operation - to set the overall chamber length. It's much faster, doesn't take a press, and increases accuracy while not requiring a gunsmith level technical education. Stoner's designs involved a lot of assembly improvements that go unrecognized. Because of that barrel extension, the bolt locks into it, not the receiver, which makes the upper and lower much less stressed. An AR barrel assembly can chamber a round, lock in the bolt, and be fired by a tap on the firing pin. A traditional pressed assembly would have the receiver attached to lock in the bolt.
This is why there is an incremental loss of weight for barrel extension designs as the receiver isn't stressed and doesn't need to be as heavy - so designers are free to use aluminum, carbon fiber, even polymer.