The case that is the largest and fills the chamber the best would minimize tilt in the chamber and settle the closest to center. But wouldn't this make the case to not fl size and keep the body as large as possible, there by minimizing tilt and keeping pressure consistent? With loosely cut shoulders on factory barrels you'd likely never match the should cut in the chamber to the shoulder on the case, fl sized or not. So minimizing neck sizing, maximizing oval so that the bullet touches the rifling would help center the cartridge. This might explain why some rifles work best that way (sloppier cut chambers) and some don't (more concentric chambers)
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