Found this in the dirt with some older items that appear to be from the late 1800's - early 1900's, little glass medicine type bottles and a piece of purple glass the looks like it could be a part of a bowl or something.
Well it does look a bit like civil war era rifled artillery shot. Look into your cities history during the war.
Ed: I don't necessarily think it's that exact shot but the right image is to clarify why I think it might be especially with the sides splayed or like that.
http://www.civilwarartillery.com/
The link resets back to the homepage. It's field projectiles, rifled projectiles read-parrott and at the top there is one that says read v parrott and it'll be the image on the right.