Could this be old militay?

[MackDigger]

It was big heavy and deep

 

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[TheCannonballGuy]

If by the word "military" you mean a piece of an artillery shell... the answer about that object is no. Neither cast-iron shells nor steel shells fracture with such a very long perfectly-straight edge -- as the object's right-side edge in the photo seems to be.

 

[HuntinDog]

I don't know where you are or found the piece, but around here it would look like cast iron sewer pipe.