It's not that a 6.8SPC gun can't be accurate. I spent good money getting ARP's barrel and expect it.
Longdayjake is referring to how the case diameter, shoulder angle, bullet length, and overall length can be selected to make a highly accurate caliber. Some features are better at it than others. The 6.8SPC designers deliberately chose not to include them because they were looking for more POWER from a 14.5" milspec 2MOA gun. Not setting a 600m record for smallest group.
A short fat case, steep shoulder, and long bullet, even in the same overall length, will be inherently more accurate - but you have to shoot it at extreme ranges to take advantage of it, much less see it. The difference is the BC, which means the bullet loses less energy over longer distances, and takes longer to go subsonic and tumble. Just a matter of what you prioritize in the features you select. That's what the inventor of the PPC case design did, and he's earned a trophy case of collective awards that many others pulled the trigger on.
Overall, the accurizing of either gun in it's caliber is about the same. Optic, furniture, and trigger varies little among the precision crowd. Without the caliber engraved on the port cover, you might not be able to see any difference. Sighted in at the same distance, most of the trajectory difference is covered with a candy wrapper.
Longday shoots both calibers, it's an informed opinion.
