Front trunnion

Because the receiver on an AK is just sheet metal, it needs some other bits attached to it to actually be functional.  One of the most important is the front trunnion.  It's the piece that holds the barrel.  Like all the other pieces, it gets riveted in.  We can't just slid it in and rivet it though, there are no holes in the receiver for the rivets, and because the trunnion slides into the receiver, you can't see the holes to mark them.  Now, I could measure, mark, drill undersize, and file the holes to an exact fit, but even typing that sounds like a lot of work.  There's a much simpler way.  Enter the Post-It note.  You can see here the three holes we need to transfer, with the Post-It note attached to the top of the trunnion:

With the Post-It flipped down, a pencil is used to find the holes the same way we all did to make textures in grade school:

Then the trunnion gets slid into the receiver.  You'll notice that I've got the magazine in place too.  That's because the trunnion locates off the magazine, and the magazine locates off the trigger guard, and that's why the trigger guard was our first step. 

The Post-It note is now outside the receiver, while the trunnion is inside, and we know exactly where to center punch the rivet holes. 

With the holes located and drilled, we have to install the rivets.  It's once again time for a special tool.  We'll call this one the Harbor Freight Bolt Cutter Rivet Smasher Tool™.  It's one of those tools who's name describes everything about it.  It's a Harbor Freight 24" bolt cutter with rivet smashing jaws.  Most people modify the stock jaws.  I didn't want to because the bolt cutters cost me a whopping $14 and I might actually want to cut bolts with them some day.  So, I made my own jaws from some 3/8" steel plate.  The skinny side has a flat face for smashing the rivet, the round side has a 5/16" dimple to support the rivet head:

With everything ready to go, I painted the inside surfaces with Duracoat so that there wouldn't be any bare metal in where moisture might get and I couldn't clean.

Here's the HFBCRST™ in action.  It works pretty slick, and smashes the rivets right over.

Here's what we end up with.  The rivets are smooshed flat on the inside, and the heads are still nice and rounded on the outside.  Even though the receiver is already classified as a firearm, it still is no where near being operable, but we're one step closer.