The sprue is created where the cut-off plate on the mold cuts the ball/bullet from the excess lead poured into the mold. On Lee molds, there is only a flat spot remaining on the ball surface; whereas on a Lyman mold, a slightly elevated (max 1/32") flat spot remains. Either style will fly straight if the sprue is centred when the ball is loaded into a cartridge or muzzle-loading barrel. Get a Lee mold and be done with it: for the price of shipping a box of a hundred balls you could have the Lee mold.