Tinker,
I dread the day that lead can no longer be used. Life will become more complicated and unnecessarily so.

Logically, if a non lead bullet will mimick the barrel wall pressure and the engraving pressure of a lead bullet, or perhaps lower those pressures, all must be well. To this end, a dual diameter drive band copper bullet would be the only way to go. It would require correct design and good knowledge of the rifling profile and dimensions. There is nothing daunting there, it is already being done for odd and obsolete calibers in double and bolt rifles. The criteria would be that the bullet be able to withstand the spin up torque without stripping the drive bands and be of the correct length and shape to perform satisfactorily on impact. The up side is that fouling will be reduced and consistency will improve. The downside will be cost because lead is so much cheaper than copper. Working lead is also cheap compared to precisely turning copper.

Daryl_S,
Forget about money being the root of all evil. I think that opinion that results from thumbsucking is. I have frequently encountered opinions that are based entirely on folklore, hearsay and "everybody knows". The bottom line is that firearms are engineering solutions and require logic and adhere to engineering principles. Magic plays no role in any solution just because it is a firearm.

The difficulty arises when anyone tries to come to a decision based on the facts at hand. We all do this every day and, usually the facts are adequate. Sometimes they are not and then we have traffic accidents, buildings that collapse, stock market calamities and businesses that go belly up. One of the greatest skills is to learn to how to identify the correct advisor in a given field. And then there are the con men.