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.
That is precisely my point. Much of what is thought of as "inherent accuracy" is related to chamber design more so than the boiler room.
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