Just some ideas.
Most of those replica gold bar paperweights are plated with about 7 millionths of an inch of gold, more or less. If that's the case and the bar is 4" x 2" x 1/2" (just a guess) , there would be about 0.05 grams of gold total - about $2 worth - not worth recovering.
Take a pencil eraser and erase the gold in a small area until you see (use good lighting) the white or gray colored metal underneath the gold. If it erases off easily with a few strokes (say, 10 strokes, or less) using medium hard pressure, you might be able to just melt the bar, gold and all, and cast the bullets. If the bar is lead with the above dimensions, and if the gold is 7 millionths thick, the gold content would only be 6 parts per 100,000 (if my math is right), not enough to cause problems in the castings, I wouldn't think.
However, there could be some antimony alloyed with the lead to harden and stiffen it. Also, there could be white nickel plating between the lead and gold. I don't know how either of these metals will affect the casting. Most of the gold and nickel could be sanded off before melting. If you do sand the bar, wear a good particle mask.
Are you sure it is lead? I have seen them made of lead, but most I've seen are brass.
If it takes more than 10 strokes with the eraser, count the strokes and report back.