Fishing Sinker Mold?

While metal detecting I dug this object up. I am not positive what it is but by going off of its shape I believe it is a mold for pouring fishing sinkers. It is metal surrounded by ceramic. In the forth picture you can see its other half which is missing the ceramic and badly corroded. The object is an inch and 5/8 wide by approximate 3/4 inch tall. I would like to confirm whether or not this is a mold for pouring fishing sinkers or if anyone may know what it is.