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Onward to the last bit of building the AK's receiver.  The last pieces of the puzzle are the rear trunnion/stock tang and center support.  Like everything else, these require some special tools.  Well, actually not, all you really need is a hammer, but it'll look nicer with some better tools.  The tools in question this time are both rivet sets.  The first bucks are for the rear stock tang.  They're made from 1/4" steel with some 5/16" dimples in them to form the rivets.  While you could just hammer the rivets over, the rivet bucks make for nice domed rivet heads.

With the stock tang and rivets in place, with one buck on the back side you start by hammering the rivets down far enough that they lock into position.  You can also see in this pic that I painted the inside of the receiver under the trunnion, so I don't have any bare metal that can rust.

Then, using both bucks, squeeze everything together to form the rivet heads.  A hydraulic press would be nice here, but I don't have one so the vice works.

Once everything is properly squished, you should have some nicely domed rivet heads. 

The very last piece of the receiver it's self is the center support.  It's essentially just a long rivet with some steel tube around it, and keeps the receiver from bowing apart.  You've got to be careful with this one, it only goes in one way.  The pre-formed side MUST go on the right side.  Instead of a full dome, it's got a flat head that is necessary to clear the safety lever.  If you put it in wrong, you'll have to grind the head down to clear the safety.  You can also see in this pic where the welds are for the inner rails.

The process is the same as the rear trunnion, hammer to set, then to the vice with a dumpled buck to finish forming the head.

And there you have it, the hard part is done.  After a few hours and several special tools, we're left with a complete AKM barreled receiver.