223AI or 6TCU (short throat) coyote rifle

[AWS]

6mm-204, no fire-forming, off the shelf dies and published data(Hogdon 2012 Annual Reloading Manual page 32). Built one in 2006, rechambered a 6x47 Rem(6mm-222 Rem Mag) barrel. It was the last cat I built on the 204case.

I would think a 6mm ARC would fit your criteria with just the change of the bolt head