What is the Fill Rate or Filling Percentage?

The Filling Percentage is the effective or usable combustion chamber volume occupied by the charge. This is also named "Load Ratio" or "Fill Rate" and can be found in good reloading manuals.

The Effective Combustion Chamber Volume is further explained here.

The volume occupied by the charge is equal to the powder bulk density multiplied by the weight of the charge. The powder bulk density can be found in our powder/propellant database.

• Fill Rate = volume occupied / usable combustion chamber volume

• Volume Occupied = charge x bulk density of powder

• Usable combustion camber volume = total case volume - volume occupied by seated bullet

Important notice: Reloaders commonly try to operate with fill rates between 80% and 100%. Loads below 80% can be dangerous as they can produce very unsteady results. Loads above 100% are "press loads". They can also produce unsteady results and often dangerous pressures.

You might want to use filler material if the fill rate is below 80%.