If they are lubed, and the dust is an issue you could set them in a cheap Dollar Store cookie sheet on top of a shop towel and use a blow drier to heat them up where the lube flows off onto the towel. Then simply relube them with some Alox and go for it.
If there is grit embedded into the lead I would remelt them and repour if you have the stuff to do so.
If simply dusty unlubed lead you could gently wash them in a disposable bowl with some soapy water using a soft brush to lightly scrub them. Let them dry and lube them up with Alox for shooting.
Mike / TX