I had gottom some "Lead" Bars from a friend of mine and figured by the hardnes and look that it was wheel weights. I melted some down and noticed it took a long time to start melting and when I would fill my .430 cal. mould it took longer to solidify. I didn't put much thought into this until I shot a few and they printed an 6 inch group at 20 yards. When I got home I weighed them. The 240gr bullets dropped at 187gr and the 220gr at 167gr or about 76% the weight. Any ideas about what it could be?

It sounds like pewter. It's sold in bars for casting toys and trinkets. It's not strong enough for bullets. The rifling strips at a much lower velocity than lead.

The longer melting time troubles me. That argues a higher melting point than lead. Both pewter and bismuth/lead alloys would have a lower melting point. A lead thermometer to get the melting point would tell us a lot.

It would be nice if JBelk were right. Pewter is 90% + tin. You could sweeten an awful lot of WW with a few pewter bars. I've been known to drop yard sale pewter into my alloy pot and only wish I could find it more often.

One more candidate is zinc. It has a bit higher melting point than lead, but is still within the reach of most melting pots. Your bullets are a bit heavy for it to be zinc, however. Zinc bullets would weigh about 2/3 of their weight in lead and would be quite a bit harder.

One way to tell is to go back to casting with your normal alloy. If you get really bad bullets, you have contaminated your pot with zinc and need to get it sandblasted.