made of cast iron, about 4" overall, small end 1/2" diameter, large end 1" diameter. I think it is a gate/runner smoothing tool. But what is it's real name?

If it were a foundry molders tool, it would probably be called a "slick". However, in my 10 years in a foundry, I never saw anything like that.
I looked through a "Monk" sand molding tools catalog, and didn't find anything there either. Sorry I'm not much help.

Mike

It has been suggested it is a "horn gate" a connection from the sprue (where you pour your metal in) to the part you are pouring
haven't found a good picture, but a chart that shows different types.