As Big Country says, you can't compare smokeless and black powder in any way! At one time, there was a "bulk smokeless powder" that could be loaded volume-for-volume with black powder and get the same MV, but at somewhat higher pressures than black gave.

Now, all smokeless powder is "dense", which means it contains much more energy per grain (weight) than any black, and therefore cannot be compared on a volume basis with black.

Even the way the two powders work is entirely different.Black powder is a mechanical mixture of saltpeter, sulphur, and charcoal. It burns when ignited, and at the same rate whether confined or in the open. When it burns it produces expanding gas which is what propels the bullet, BUT only about 40% of BP is converted to propellant gas. The rest remains as a solid mass, most of which sticks to your barrel walls as fouling! On the other hand, smokeless powders are made from nitratedcellulose ("guncotton") or nitrated cellulose andnitroglycerine, and when it is ignited by a primer in confinement(inside your gun), its' molecules rearrange themselves into more stable compounds in the presence of heat and pressure. These product compounds are mostly gases and H2O vapor which occupy much greater volume than the solids from which they evolved(the powder charge). The greater the heat, pressure and degree of confinement, the faster smokeless powder "deflagrates" into more gas. So basically, when used as a propellant in a cartridge, smokeless powder doesn't even "burn" in the same sense that black powder burns!

This difference in powder types also explains how a very small change in the amount of smokeless powder in a load can make a relatively large difference in the peak pressure and even the accuracy of a load. This effect is totally different from what BP charge changes do.