hillbill, What I believe you have is the cartridge for the military's relatively new FN P90 weapon. If you happen to be a sci-fi fan, watch Stargate SG1 on the TV and you will get a look at the weapon.
While the P90 is not available to civilians, I think that there is a firearm now that is. These cases keep showing up on ranges, so there must be one out there.
I believe that this round was developed by necking down the 10mm Auto round to .22 or .23, not sure about the actual bullet diameter. It is supposed to be a real screamer with velocity in the 2800-2900 fps range with a steel core penetrator projectile.
Wish I could tell you more, but maybe this info will put you on the right track. :-)