Bob I would say stick with the production bullets for a couple reasons. They look like RWS R50 and if so they are super soft annealed lead and free of voids and a fancy coating to boot.

I'm afraid cast boolits would be inherently too hard and at these spins rates if the was any void or inclusion the would be going around like an egg beater.

Did he happen to say what a mandrel was worth to pay for outright?