What different methods are used for forming the rivet head?  Show pics if you have them!

I don't bother forming them round. I mash them as flat as possible, by mashing a little, then re-setting the press to make sure it is perfectly straight. This way the rivet head mushrooms symetrically.

When done there will be a pattern on the top, I usually hit it lightly with a file or sanding block, then break the edges...takes like 2 minutes. Then I call it done.

Hmmm actually I do remember one time I had some differnet rivets and I mashed it flat half way, then used a piece of metal with a cup for holding the round rivet heads using the Plinker jig....it came out good, but I think you need longer rivets with more material to form into a round head...I only did it once and it looked nice and round. Now I just use the above method.

I just completed smashing the rear rivets on my first build about 10 minutes ago.  Basically, I used a dremel to form a bowl on a crush plate that came with a trigger jig.  After I made sure that a rivet head fit in it, I put the crush plate on the other non-crushed side and put the entire rear section in a vise.  Came out perfectly.