When cases have been reprimed, put gunpowder into them. Powder is measured in grains, and there are 7,000 grains to a pound. Use a scale that is accurate to at least one-tenth of a grain. The amount of powder needed is listed in the reloading manuals powder and bullet manufacturers offer. Follow these directions to the letter.
Rifle cartridges operate at extremely high pressures, so be prudent.
Once the powder charge is funneled into the case, seat the bullet. Follow the directions when adjusting the seating die. With some cartridges, it is necessary to have the mouth of the case crimped to the bullet. The seating die can be adjusted to crimp or not. That's all there is to it.