Well for cryin' out loud put the hammer back down. There's nothing that irks me quite so much as seeing an otherwise competent blacksmith swat the daylights out of a piece of iron, then pitching the piece back into the fire, the barrage is punctuated as he whacks the hammer, handle first, onto the anvil face to drive the head back into the handle.
Hickory is a remarkable material.
Make certain before you use a sledge that the growth rings are oriented as in Fig.1. This guarantees the greatest strength and flexibility in the direction of greatest stress. Next, make sure that the handle is wedged in both directions. If you are creating your own handle from scratch, a few caveats. First as mentioned, you need to pay strict attention to growth ring orientation and grain straightness.