These darts are really special and they have a very weird rattle-thunk when they hit the board that is way unlike any other dart I have ever thrown. They are old Accudart Penetrator's that have removable graphite points. The rattle comes from the fact that the graphite points are held in with collars as if they were hammerhead style moving points, but there is not back and forth movement. They spin certinly, but no jackhammer type movement. The thunk is different because the graphite points are pretty thick all the way down to the beveled point. You can see a better pic here.
The darts in this pic aree configured with medium length scalloped nylon stems and standard dimplex flights. I have been moving more and more to this kind of setup.