I am starting to build a couple of clocks for an outing sponsored by our state fish and game department. One of the clocks is to have 38 caliber cartridges for the 3-6-9-12 positions. The others will be .22 cartridges. I may have to cut them off for the thickness of wood. I do have a lot of wood, as if woodworkers always face a shortage of wood. My question- when I determine the center of the face, what is the best way to lay out the 12 positions? This one will be a wall clock. The other will be a desk clock. Thanks.