another interesting ref. site:
Solid shot essentials
i noted in there that grapeshot was frequently cast in gangs, ie. like pearls on a string, rather than individually, thus no sprue, and ordinance regs required them to be tumble finished which would have reduced or removed any mould marks and obscured the end details where the individual balls had been broken apart. the oval grape could easily have been produced this way. as it notes, grape did not come into contact with the bore and so could be quite irregular, where odd shaped round shot could scrape or lodge in the bore, damaging it. grapeshot was required to be made from cast iron, tho lead was an accepted alternate. canister, which later replaced grape, used lead musket balls.