With the variety of powders and barrel lengths that one can encounter I am wondering why there has been no conclusive data posted about the effeciency of propellants in various bbl lengths?

I don't mean velocity, I mean at what point is the powder is not being completely burned in the barrel. It would seem like this would be the most effecient load for a given rifle. Any more would be wasted. I understand that the best accuracy may not come from the load that provides complete burning of the powder, but it would give a very good starting point to start backing down the load.

Maybe this research has been done and I just missed it?