Below is a photo of some experimental which were given (gifted) to me about 10 years ago by Jean-Paul Dennis, formerly of FN. The background story is that those are remains from his work on FN P9.0 project which resulted in development of the 5.7x28 ammo and associated FN P90 and Five-seven weapons.
L to R:
4.5mm based on .22WMR, h/s “Rem”
5.7mm based on .22WMR, h/s “Rem”
5.7x24mm frangible, h/s “5.7x2* FNB 95”
5.7x24mm ball, h/s “5.7x2* FNB 95”
commercial 5.7x28 FN for scale
I have no idea if those are genuine or not, but thought I can share this foto because of recent discussion about FN