Yes, I clearly read "weight or volume." Based on granule configuration "volume" is a pretty poor measurement of smokeless propellent, although ball powders generally have pretty uniform volumetric configurations. Stick and flake powders...not so much.
And even then, the energy contained in the powder comes out by the transition of solid to gas, so the powder that has the most potential gasses in the solid is the most "energetic." Which tells us nothing about burn rates or energy transfer to the projectile.
In ballistics we can often show that the "most energetic" powder might not give the best ballistics in a particular cartridge in terms of energy at the projectile. If the burn rate is wrong (something completely seperate from energy) then the ballistics will be affected.
So unless the OP is really asking how to make the most energetic pipe bomb, I thought a more in depth answer was appropriate.
Machine guns are awesome until you have to carry one.