Mac - around here the wood of choice for the heads is Live Oak. It is a twisty, gnarled, member of the oak family that isn't good for much. Around here it is bbq and firewood most of the time.
But for as long as anyone can remember it has been a favorite for tool handles, mallet heads, chisel handles (socket type) and anything else that can use a smaller piece of wood.
All the carvers around here use it for their mallets, and also make the old fashioned pattern maker's mallets as well as the cabinet maker's mallets. As a testimony to its endurance, I have a buddy of mine that uses one his grandfather made in the '30s. It was made as a utility mallet and was obviously used to wail the snot out of anything that was in reach.
This link might work - it's a bowl made from Live Oak. You can easily see the interlocking grain. Don't look at this picture and think that's an unusual piece of wood. It's the norm.
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This stuff grows around here every where. In the next couple of months I will be making some traditional pattern maker's mallets, probably with either kiln dried white oak heads or Live Oak, handled with some mesquite. Are you making yours for gifts or for personal use?
Robert