JesseH1234 said:

Followup question: Say you had a 6mm fmj bullet, same nose shape, same overall length, same velocity; one was a 90 grain boattail, the other a 100 grain flat base.  Which would retain energy better during supersonic flight? 

Depends on the exact shape. The 90gr bullet would need a 10% better i7 than the 100gr bullet to equal it. That is possible, as I mentioned, optimizing boattail shape has earned me the bulk of a 15% improvement in drag, and that was just by optimizing boattail shape, not against flat based projectiles.