If the bullets are intact, you need to cut the plating.
For 'TMJ' style and plated bullets, I use the cutters on some hefty linesman's pliers to notch the jacket, or actually cut the bullet into two pieces.
I use different alloys for different purposes. For some things, range lead is perfectly fine. It isn't difficult to clean, either. A quick wash and some time to dry, are all you need before smelting.
I know what's in the range lead just as well as (or better than) when I buy supposed alloys from some random dude on an internet forum (which I trust far more than places like Gunbroker or eBay).
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."