Ben - just look at the chart to see the answer to your 600gr. ball at 1,500fps question. Re-read Greener's book about rifles. He lists the 7 dram load as being the biggest of 3 loads in 12 bore. What exactly are you planning to hunt?

The .577 is a hunting rifle - the 12 bore is both a hunting rifle and a stopping rifle. There is a difference.

Marrakai - thank you for the expanation concerning the powder charge discrepancies.