I kind of disagree.
These projectiles are tough and can stand a lot of handling. However, you never know that where you have it stored could not possibly catch fire and then cause the shell to explode. If that were to happen and someone were to get killed or injured you would be in deep trouble. Best to keep outdoors somewhere.
Be careful of who you show this to and tell. These things are no laughing matter to law enforcement. If they were to find out you had that shell you can bet you would get a visit by the local bomb squad and they would take it and others you may have and explode the whole bunch, and you could also possible be prosecuted for having a bomb, and that is no joke. ATF can do anything they want.
I also have an unexploded cannonball. I have already defuzed two safely. I keep the current cannonball in a bucket of water. I have removed the borman fuze which is made of zinc and comes out usually in pieces. I have also used a toothpick and cleaned out the hole in the brass plug so water has gotten to the powder. I did this after the death last summer and sever injuries to another (expert) the year before when they were defuzing projectiles. I didn't realize that once powder dries out it is as dangerous as before.
I found a kind of squashed .54 minnie still in its brass cartridge. The cartridge was split and underground, and also it was in a dried up man made lake bed, anyway, I emptied some of the contents of the cartridge and hit it with a match and there were still some sparkles. Not like good powder, but nevertheless, there were still some remnants. I have read that black powder tends to worsen over the years, and by worsen I mean get more and more dangerous.