I have a CZ550 magnum in .375 H&H just wondering if they use the same bolt head size for the .416 rigby as the .375 H&H?

Do they have larger bolts for the 505 gibbs or 404 jeff?

Yes its the same bolt, but the facing off of the bolt for 375H&H is smaller than rigby

If you wanted to turn your 375H&H into a rigby you would need to get the bolt face opened up and the extrator altered

And there is enough meat on the bolt face to open it to 505 gibbs and even the 600 OK as well which is bigger than the rigby again.

reg S&F

As I understand it the cz550 has only one bolt diameter size for all calibers ~ .700.

A couple years ago I heard rumor that cz was considering making a larger (longer & wider )action with a bigger bolt diameter....nothing so far.

Gunsmith Mike Scherz at Gila River Gun Works makes .750 diameter bolts specifically for the cz550 action.

Gila River Gun Works

Best Regards,
Dave

Ok thanks for the clarification