The tip is indeed a pop rivet. The ones in the picture are aluminum. The ones I made for Nationals last year had sharpened stainless steel tips. I had a few tips left over and changed out some of them for a few people at Nationals this year. The sharp tips don't work so well for throwing boomerangs to your hand. The idea was that they would do more damage to the target top.
The crown is sized to accept a bottle cap. It helps to identify your top and also helps protect the crown from being split. A good hit will knock the cap off which will get you points.