Stupid mistake. I can't understand how a sober person could load and chamber the wrong cartridge for a rifle ...

The only rifles I have where I think this could happen, and as a result I am EXTREMELY careful with them when assembling these rifles, are my multi barrel, multi magazine, multi bolt head Mauser M03's. Where theoretically I could use the wrong bolt head for the wrong barrel etc.

I know I have had eg a .435 P-H cartridge mixed with .375 H&H Magnum cartridges, and identified it and removed it from the lot. No idea if it would chamber in a .375.

A bit of care works, and sensible practices. Fingers crossed, just in case.