There is indeed such a thing as inherent accuracy--and the 6mm PPC is a perfect example, along with several others designed for accuracy. I have explained a lot of this in my articles and books.
A big difference tends to be in the shape/dimensions of the chamber throat, but there are other factors.
It seems like you are deviating from cartridge design and discussing rifle chamber design. If a '06 or .270 Win chamber is built to the same dimensional tolerances and throat dimension:bullet diameter ratio as, let's say the darling of the moment, where does "inherent accuracy" come into play?
Full disclosure... love me my 6.5x55, 30-06, and .270 Win. Old School Stuff.
See my comments about the 222 vs the PPC cartridges in benchrest competition.
