I've used the Game kings a few times and they can be effective. In .338 I've only used the 250 weight bullet and it has worked both times I fired them into moose. At just over 200 yards the moose stopped one without broken bones. At twice that distance the bullet made it through the meaty parts of both shoulders and exited.

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This bullet was taken from the bull it killed at the shorter distance. It appeared to be intact when I found it, but it came apart as I scrubbed the tissues off it. The core had been 'feeding out' as it penetrated and expanded. In the case of the longer shot, I found a hole in the snow beyond the animal. The jacket was just below the surface. The core had apparently been loose at the time of exit as it had continued into the drift.

They work, but there are better bullets; I would be concerned about what might happen if a big bone was hit.

Sometimes, the air you 'let in'matters less than the air you 'let out'.