Looks good Thomas.Bill92
They can be made in any shape and hold as many balls as you like. Oblong. Round. Cloverleaf. Shaped like a fish. Carve a design or do some wire inlet to fancy it up. Stain or paint it. Whatever. Get creative!
As has already been said, make the board a little thinner than the diameter of the ball so that the patched ball can stick through a bit beyond the wood and be easy to center in the gun's bore prior to ramming it home.
I use a fowler for small game and so do not have need of a bullet board/loading block. However, for big game hunting I like a board with only 3 round balls. Starting with a loaded gun, that makes 4 balls ready. I figure that should be plenty for a day in the deer woods, and it doesn't weigh too much. I hang it around my neck and tuck it inside my shirt so it doesn't dangle and get in the way before I need it.
For target matches I might use a board with as many balls as needed for the course. Or, at least half as much depending on the size and weight of shots needed. Make two.
Of course, I carry extra balls and patches in my shooting bag.