When I was in the SCA, we had a tool which was a piece of steel with a hole drilled through. It also had a shallow dished hole. We were able to get rivets at our local Ace hardware back then. I used them to make my helm. The seating tool was used to make sure there was no gap between the two sheets and the dished hole on it was used to make the rivet "swell" in the hole so the pieces wouldn't shift. Then we used the round part of the Halloween hammer to flatten the rivet. The guy who taught me was good enough, he didn't bother with the tool. If you were joining two pieces of armo that needed to rotate, like a knee or elbow piece, you put a steel washer between the two pieces of metal you're joining. Another thing they used to do was use pieces of wire as rivets on every other link on their chainmail to make it nearly unbreakable. The unriveted rings were welded solid.
I'm going to try this, and I'm planning to create a tiny hollow at center, on the side I'll be hitting. Gonna use a center-punch, and possibly drill a small hole (1/16 inch, 1.6 mm deep). I think that may help the metal spread out more easily with less effort. Note: Will probably need to grind or file the top FLAT before making the dimple.
Coo! What I personally do is start it off with the flat side and finish it off with the peen side. The peen side squishes the material a little more for a tighter bond. Starting with the flat side just makes it go a little more ‘quick and dirty’
Sometimes theses rivets loose easy but I use it to put small things together reason theses methods is trying to make things without power tools as possible.