RE: Why are some calibers more accurate?
Vapodog, I used to do a little Benchrest shooting years ago. I sold off all the guns to help pay for the house and now many years later I'm just getting back into shooting. I haven't done a lot of big game hunting but that's the direction I'm heading. I ordered reloading equipment yesterday based on your advise and will be getting a varmint rifle early next year as well.
This much I feel confident in saying. Any caliber can be a very accurate cartridge, yes, even a .25-35 Winchester, if it gets the craftsmanship and attention to detail that the 6MM PPC gets. I owned a .308 Tight neck on a 40-X and Hart barrel and McMillan stock that normally shot in the .20 range. The reloading was done by a buddy and I never got into that, all I know was the ammo was expensive!
I believe you're absolutely right when you say that there's very little difference in accuracy of different calibers. Certainly none that a big game hunter will ever see.