First of all, welcome to the forum. You came to the right place. There are many knowledgeable people here and many of them are experts. I'm a million miles from being an expert but I will relate to you one thing that I was told by archaeologists who were digging for artifacts @ Fort Independence (Castle Island) about 40 years ago.
We were doing some excavating for the fort's renovation when we found an un-exploded cannonball. The fort was built in the 1600s & was not fired on or fired from, but the cannon ball looked like yours with the "plugged" hole still intact. (hole to fill with gunpowder). They told us that those things were still dangerous even after all those
years, & we were lucky we didn't strike it with the backhoe because it could have exploded. Up until we found that, they had only found an old shoe & some pottery fragments & nails. Needless to day, they were very excited for the find. So, to make a long story short, be careful with that thing until you have it checked out by experts.
Good luck. Happy hunting & welcome to "TNET". Cheers !!