Im gonna forward this page to a buddy but my guess would be a oooollllld school lead melting pot... Or some sort of ingot maker... Ill post up if someone who knows tells me for sure..

Ok truth is out. It is a mold of sorts. Was used to mold coal dust into chunks. I'm on my phone but ill copy and paste the stuff on it tomorrow

This is from a ooold reloader so he saw them as a youngster...

HAHAHAHA - I KNOW!!!!

Many years ago coal was ground up course and mixed with water into a thich paste. It was then pressed into these molds and the water was squeezed out by clamping the top on. The punk was then sun dried. They fit into the iron stove to be burned for fuel. The holes let the air flow through for better combustion. It has been 50 years since I have seen one of these.

Another
Right on Griz! My grandparents on my dads side had 10 of these moulds. Grandpa told me stories about how his dad would buy a railroad coalcar load of coal at a time. He and the hired hands would haul coal for 2-3 days at a time in the spring to stock up for winter. Handling coal this many times would create buckets of dust and small chunks. All spring,summer, and into the fall they would make these coal cakes. They were used for starting and rekindling heating and cooking fires during the winter. ( So this is a mould but not a lead mould.)

Another
When I was young my Grandparent's home was heated with coal and they had a coal stove. That mold exactly what Griz said it is and molds like that were used by almost everyone who used coal in their home. The "coal pies" were usually used in the coal stove since it smaller than the coal heating furnace.

The coal pies served 2 purposes. Like Griz said the pies would fit perfectly in the stoves and using that mold was the only way to make all the coal dust left in a half empty coal bin useful. It allowed you to turn useless dust into a productive fuel again.