Mauser owns the majority of the John Rigby company.

The choice of cartridges chambered for the Rigby Mauser is logical based on classic choices. Plus classically popular cartridge choices. .275 Rigb of course. 7x57 in the Mauser. .308 and .30-06 are popular in the USA still and everywhere through out the world. 8x57S was and maybe still is the most popular cartridge in Germany. 9.3x62 is the best driven game cartridge in a bolt action.

Probably same line up for economies of scale. Commercial businesses exist to make a profit.

My guess is we will over time see some additions. Perhaps some divergence in the line up. And maybe some cartridge deletions over time. So if you want one now, get one.

No doubt prospective customers not seeing what they want in the range, will mke their desires known.

.270 Winchester, and 6.5x55 are two that are popular but not there. And some of the classic magnums that fit the action.

I'm more than glad NOT to see any "Ultras", "Short Magnums" or other "trendy" must have instantly redundant modern choics. Old and a hundred years old or at least fifty years old for me.