Its always been my experience and teaching(from the US Marine Corp, hunter education, and other persons) , that accuracy is dependant on four (4) things: the elements(humidity, rain, wind), bullet design(B.C., center of mass, etc), rifle itself and the shooter. The casing has little to nothing to do with accuracy.
Its like comparing a 2800fps 150gr bullet from a .308 Winchester cartridge to a 2800fps 150gr bullet from a 30-06 Springfield. If both bullets are the same, both rifles the same - then any differences in accuracy has to be the elements and the shooter. The casing doesn't interfere with the bullets path once it leaves the barrel. In fact, once the bullet leaves the casing - no longer can it interfere. The only variance would have to be the "luck" factor.
In logic, the 270 is no better, or no worse then any other cartridge. Its just another casing designed to hold powder and bullet together until fired - then all it is is a gasket to keep the pressure in the chamber and barrel. The differences between .257, .264, .277, .284 and .308 inches are moot, same with any arguments with the cartridge itself. ...in truth, its quite asinine.
One things that is an absolute: bigger bullets make bigger holes.