Here are a few thoughts in relation to your last post. First, the 350 Rigby and the 333 Jeffery are both almost identical in case capacity to the 338 Win Mag, so depending on the pressure level that you load to it is possible to reach that level of performance ( BUT NOT AT ORIGINAL PRESSURE LEVELS ). Unfortunately the available brass is a bit soft for these pressure levels generally. In the case of the 333 good brass can be made from 330 Dakota brass, which I use in my Jeffery.

Second, the Ross case is good for single shot actions due to the small rim for easy extraction. Capacity is almost identical to the 7MM Rem Mag. Good quality brass is available from Buffalo Arms (on extensively modified 348 Win brass), and is much cheaper than Bertram. Bell basic brass is available as well. Whether you call it the 280 Ross or 280 Halger makes little difference, as the cases were so close to identical.

The 280 Jeffery would be an easy reform of 7MM Dakota brass.

As to the 275 Rigby Magnum, there are several possibilities. Rigby loaded their version of the 7x57 and called it the 275 Rigby. They also had a higher velocity loading of this round, which I seem to remember was called 275 Rigby Magnum at times. Additionally they had a 275 No 2 Magnum (7MM Rigby Flanged Magnum), and in the index of COTW they list a 7MM Rigby Magnum as a smaller case than the 275 No2 Magnum.

It is all a matter of how much change is acceptable before you no longer have the original cartridge, but a wildcat. Half the fun is using the original ballistics as well as the original case dimensions. Sounds like you have a great project with the Hagn action. Martini-Hagn does some beautiful work!!!! As to the 280 Ross vs the 275 H&H, either would be a great choice but I like the idea of a non-belted case if I am going to try and get away from the modern rounds. Here is the completely original M1910 280 Ross that I hunted with this season.

Good luck,
Jim