Making a mold for sling(shot) might be best. Ballistic balls can be stanardized much easier. You could eventually decide on one or two diameters as previously suggested. Sinker molds would have to be made in many sizes depending upon the type of fishing, bait,depth of the water, strength of the current etc. Fer instance, I use a lead head jig for surf fishing. Depending on the conditions I might cast one @1/2 oz thru to 3 oz..

From time to time molds for sinkers and jigs come up for sale on a surf fishing forum I'm registered on. There is interest, but they're not knocking each other down to buy these molds. Good Luck