What 300six has to say is true, but the fact is, heart wood and sap wood handle vibration and stress in different ways. When you have a handle that is half heart half sap, you have a handle that has two very different types of wood in it. I would caution you to either go heart wood or sap, not both.
One more thing, was the tree 'down' out in the wild? Please be careful of dry rotting. Inspect the wood carefully at all stages of working.
One more thing, was the tree 'down' out in the wild? Please be careful of dry rotting. Inspect the wood carefully at all stages of working.