It's a .404 Jeffery Light. Same diameter bullets, just 50 grains lighter in standard loads. Fits better in a standard length action.
I have a Jeffery, and I want a 10.75x68. I shoot 400's at 2300 fps in my Jeffery; I can't fathom how an equally constructed 350 at 2250 fps would demonstrate any diminished lethality.
Phil -- your friend's rifle sounds like an absolute dandy
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DN