That is 7000 grains WEIGHT to a pound. Remember that substitutes are measured by volume, not weight. a container which will hold 20 grains WEIGHT of black powder, will hold 20 grains VOLUME of substitute powder. That 20 grains VOLUME will not weigh 20 grains on a scale.
Generally speaking, you will get more shots per pound of substitute powder than from real black powder. Sometimes a significant number more, sometimes not enough more to make a dent in your wallet.
Pops