My two pence:
The theoretical optimum shape for a supersonic body is well known, the sears-haack body
Bullets tend to deviate slightly from this shape as a practical necessity for use in a firearm, for example, bullets need a cylindrical centre section to form a good seal in the barrel and to keep them aligned with the axis.
So I would have thought that to improve a bullet, you want to bring it closer to the optimum shape whilst still making it useable in a firearm.
I always wondered why bullets don't have more of a pointed tail though, I can't see how it would affect propulsion down the barrel.
PS: Those "ribs" that you mentioned, are you sure they aren't markings from barrel rifling? Adding texture or otherwise increasing surface area rarely decreases drag. Or perhaps they are there for another reason other than to reduce drag.