av, the 7mm-300H & H was also tried my Keith, and others.. As near as I can tell it was called a 280 Dubiel.. Keith and Harry Snyder used this caliber a good bit in the 1930's.. It was Elmers coyote, antelope, deer rifle for quite a while as near as I can tell.
From all I read, they merely necked the old .300 H & H down to 288 Caliber and had the .280 Dubiel or 7mm/300 H & H, but the used 288 dia bullets instead of 284..
