I have a TAC6 wildcat. 6mm wildcat based off 6.8 brass. $249 for a barrel. Sweet little round too. AR15 Performance has the barrels. He also has the dies available too. From the guy who designed it:
This was my idea of a perfect tactical cartridge 0-600yds with ease. It is capable of shooting super light bullets at small varmints, 75gr bullets at yotes, 95-108gr long range target bullets and 80-90gr hunting bullets at deer and hogs. The Tac 6 with 105gr Bergers will hit around 2700fps out of an 18"barrel. The TAC 6 will beat the ballistics of the 224 Valkyrie, 240 Valkyrie and the 6.5 Grendel.
http://www.ar15performance.com/inc/sdetail/38010/48383
He's got another 6mm wildcat based off the Grendel too.
So my question, when is a big ammo manufacturer going to come out with a 6mm AR round? I wouldn't be surprise to see Federal do it, since their .224 Valkyrie has been so successful.