Just some measurements.

280 Ross. Case Length 2.59" Cartridge L 3.50"
375 H&H " 2.85 " 3.60"
404J " 2.87 " 3.53"
416Rigby " 2.90 " 3.75" and 3.72" has also been given.

Going by these I would think your Ross has not been opened up like they did with the Standard M98 action to accommodate the 404J and some 375H&H and the odd 416Rigby. My thinking is that any of the ammo of the day had the bullets seated deeper than what most do today especially in the Rigby.