What did I find scuba diving?

Hello all, I was pointed to your forum because I found something you might be able to help me out with. I was scuba diving in the St Clair river and found this item. I was told that the military did some practice in the area back around WW2 and didn't know if I found some sort of undetonated artillery. Who knows could be a sinker for all I know. Anyone have a guess?

 

Should also note that it is 4" across and 8-9" tall and is pretty hefty in weight.

 

I don't think it has anything to do with WW2.but might be wrong. it's surely not a shell. if it was it would be the center part and the cap is missing. so it would of been shot, but i doubt it is.