The tightest groups I've ever seen fired at the Nosler Ballistics Lab were with the 200-grain Partition in the .300WinMag.
The barrel was on an UltraLight Arms action and the four five-shot groups were: .000", .000", .000" and .000".
Holy CRAP!!! Impossible, but absolutely true.
Hey, I was standing there ... what can I say?
Blessings,
Steve