onthedrums, the biggest difference are the parent cartridges. The PPC is an offshoot from the .220 Russian which is the child of the 7.62 x 39mm. The Remington BR cartridges use the same concept, but based it on the .308 case and I would imagine the advantage in brass and its cost would still go to the BR. If nothing else there is always 7mm BR brass that can be necked down to 6mm. Another short/fat idea in 6mm that could be the ticket is the .243 WSSM. You would get a lot of flexibility with bullets and powder selection might find benchrest accuracy well below maximum pressure with high density loads, maybe keeping throat erosion to a minimum while getting performance better than the PPC or the BR. If I were on this quest for a 6mm gun for benchrest and field applications ready if needed, I think I would investigate the .243 WSSM further. Brass will be plentiful and there are already several base rifles available.