Store-bought sledge handles often break after a season or two, so I make my own tougher, rot-resistant handles from a locust stave.
In the wintertime, I split a 3-foot, straight-grained section and leave it to dry by the woodstove. (Sledge hafting has to be winter work, of course. If you fit the handle in the summer, it will shrink and loosen from the heat in the dry winter air, and your creation becomes dangerous.)
I use a draw knife to round the handle into an oval shape with dimensions of about 1 ½ inch by 1 inch at the grip end, tapering to a slender seven-eighths-inch neck, round in cross section and located about a foot from the hammer end. I then increase the handle’s diameter to a bit larger than the hole in the head, scrape the haft end of the handle down to exact size and secure the head with a locust wedge. The taper in the handle allows flex on impact, which keeps the handle from splitting.