It's actually a .222 Remington Magnum necked to a .204 diameter bullet.

I built a similar one three years ago by altering a .222 Remington reamer and proceeding to make a chamber and then a sizing die. It's a very fine round seeing velocities well past 4,000 ft/sec and seriously little recoil. Accuracy is good and the Pdogs just vaporize.....hence I named it the 5MM Vapodog.

I wouldn't begin to forecast how sales will go....I think Hornady (the Mfr. of the ammo) has made a big mistake by not using the .223 case.....time will tell.