70 grains of black powder behind a round ball is a nice balanced load in a .50 caliber muzzleloader. Adequate for deer at reasonable ranges.
It also has a sort of mathematical symetry to it:
a pound of black powder contains 7000 grains = 100 x 70 grain charges
.490/.495 round balls come 100 to the box
patches usually come in bags of 100
#11 percussion caps are sold in tins of 100
Everything runs out at the same time. Neat.
Watch your top-knot.