How to Measure Case Capacity?

The simplest and most common method uses water:

Water Filling Method: Start with a fired case, ensure the spent primer seals the pocket (or plug the flash hole), and weigh the empty case. Fill it with water to the rim and weigh again. The difference in weight is the case's water capacity in grains. For example, if the filled case weighs 430.0 grains and the empty is 375.0 grains, the capacity is 55.0 grains of water.

Tips for accuracy: use distilled water and a dropper to avoid air bubbles. Measure multiple cases and average. Generally, heavier cases have less capacity, so sorting by weight helps estimate capacity differences. However, weight alone can be misleading across brands due to material differences. Water measurement provides direct volume.

Modern tools like the Bison “Case Volume Gauge” use powders or plungers to measure volume without water. Advanced reloaders input measured water capacity into ballistics software like QuickLOAD PRO for precision. The key takeaway: know your brass—be aware if your brass has a smaller or larger capacity for your cartridge.