Lead Free Airgun pellets

I've been coaching JROTC air rifle teams for a few years now. Last year, we were ordered to switch to lead free pellets.

Started up this year with some of the standard Daisy target pellets and also some H&N Sports pellets marketed by Champion's Choice. The Daisy ones were real problematic through our current rifles, but may work better in the Crossmans we will be fielding soon. The Champions choice ones seem to do about as well as lead except that we have a lot bounce back out of the trap and they don't deform like lead, obviously much, much harder.

Both say they are a tin alloy. I think one said there is some Zinc content as well. I salvaged the lead ones we used to shoot for making muzzle loader bullets. I would think these being high in tin would be good for alloying, but don't want to try if there is zinc in them.

Anyone know what alloy is generally used in these things?