I just snagged an ANIB ZKK 602 .375H&H in a trade.
It had about ten rounds through it when the previous owner decided on a rifle with less recoil. Snicker...
It shoots great in .375, and is very reliable so long as you cycle the action BRISKLY. Otherwise, the brass hangs on the right side receiver bridge. When cycled briskly, ejection is dramatic. The brass flies about eight feet.
I find that it is causing the brass to spank the outside of the rear bridge of the receiver a bit upon ejection, but this can be alleviated by a bit of removal on the metal in that area.
Dane Burns has witnessed the same phenomena on his 550, and is working out a formula for the removal of the material in question. It appears that a longer ejector or one with a different face angle is not the answer, but I have not actually tried that yet.
Mine is getting converted to a .505 Burns over the next couple of months. .505 Burns is essentially a .416 Rigby case blown out to .505.
Ashley Emerson has warned me that the factory stocks tend to be a might fragile, and suggests getting a better quality stock either in composite or laminate wood.
Overall, I like the action very much. It is smooth, has a decent trigger, and is very accurate.