Just how difficult is it to manufacture automatic weaponry from scratch?

[MT2008]

Originally Posted by Mazryonh

If the knowledge is really widespread, then why hasn't someone tried to manufacture the "AK-47" of SMGs ideal to the purposes of criminal/terrorist groups? Something cheap and easy to clandestinely manufacture and easily rechambered to fit local ammunition (as well as easily concealable) would be well suited for them, especially if arms traffickers prove unreliable.

Didn't I answer this question already? What would be the point of trying to manufacture full-auto AKs when there are 100 million of them in the world and they can be illegally purchased/imported with such ease? It would be redundant.