As posted in r/whatisthisthing, that appears to be a mineral specimen of marcasite, not a cannonball.

You might try posting this in r/whatisthisthing. That sub has some astonishing experts.

Get in touch with the Portable Antiquities Scheme, they'll be able to help with dating, identification, and title (especially important for the ring, which as theomeny says, may be treasure in the legal sense which it is unlawful to keep without reporting it).

Having your objects recorded in the scheme means that the information is also available to archaeologists and historians, which is very important for future research.

The home of the Portable Antiquities Scheme is here: https://finds.org.uk/

If that really is a cannon ball, it is possible that it still has gunpowder, and is therefore potentially very dangerous. I don't know what specific agency you should call, but a local museum or historical society should be able to tell you who can deal with unexploded ordinances.

I work in a museum in the US, and we occasionally have thing like this happen. In the meantime, leave it alone.