Black powder happens to have approximately the same density as water and cartridge case capacity is often given in grains of water.
For example, the .357 magnum case holds 27 grains of water and according to Howard31, measures 27.5 FFg and 28 FFFg black powder.
Want 45 grains? pick up a .30-30 case and use it for a measure. It holds 45 grains of water.
Want 69-70 grains, a .30-06 case.
Want to measure 294 grains? Pick up a .50 BMG case.
Here's a link to a list of common cartridge case capacities.
http://kwk.us/cases.html