Just a friendly reminder.
Rule # 9: We do not discuss copper and/or jacketed, plastic/polymer tipped bullets, sabots, power belts, or other 'plastic-wrapped' bullets. Smoothbores using plastic wads and steel shot are an exception to this rule.
I doubt it would be a problem, but You can take a regular ball and one of your bullets and do a side by side fingernail scratch test. This should give you an idea of how hard they are. You could also dilute them by only adding X amount to a pot full of pure lead. Rather than melting and casting them all as a single batch. Or you could single batch them and keep them segregated in case they don't pan out. I often take scrap lead or unknown lead and make pumpkin balls out of them, it eats up the lead fast and whatever I shoot the pumpkin balls out if doesn't seem to care..
P.S. I wouldn't cast them into revolver balls unless they are soft.