A steel tube with a steel rod threw it and welded into place, hard wood core
plugs held in place by bolts threw tube, more distributed weight then a wooden
or fiber glass handle and the added bonus that should the head miss the target a killing blow may still occur do to blunt force by the solid steel handle.
The tube would weigh roughly 6lbs on its own do to thickness and the bar
weighs roughly 9lbs. The bar is an old tie rod from a car and made of high carbon steel while the tube is from something else though I don't know what.

A simple was hammer idea that popped in my head so I used paint to
doodle it up quick like.