For the record, IMHO a cracking good cartridge for the action would be the 6.8mm SPC necked down to 6mm, fit a 1:11 barrel for up to 90gn monometal bullets. This would really be a pocket 243.
The 6.8 necked to 6mm with no other changes is the 6mm WOA (White Oak Arms), a popular cartridge for Highpower competition in AR match rifles. Lots of load data available and easy to form. An "improved" version is the 6mm PDK. Less body taper and the shoulder moved forward a bit, and shorter neck. I have one of these and it is scary accurate with 87's or 105 Amax's. There are several calibers in the PDK family that maximize the SPC case volume
