I was looking for a modular rifle last year and found alsorts of anomolies with bolt faces and magazines so settled in the end, not by choice at the time I might add, for a Steyr Luxus.
The same bolt and magazine can be used for 22-250, .243 and all the other cartridges with the same head size.
I have a .243, .308 and a 30-06 barrels for mine and have nothing to change except the barrel when I want to use either calibre, and each barrel came with it's own integral picantinni rail so no saddle mounts needed.