Tumbling has never gotten the insides of case necks really clean for me, even with nut shells and added cleaner. Maybe ceramic would. Usually, my cleaning consists of wiping them off with a rag to get any grit off.
When I FLS, I dip the necks in powdered mica or lately one of the little tubs full of powdered lube and beads. That ought to be enough contamination to stop cold welding.
