A Quality Control Process
A quality control step every reloader should take is to weigh each and every finished load. If each load is within a window of a few grains, you know that you have dropped accurate powder/shot payloads. In order to do this, you will need a scale that has at least a two ounce capacity, such as the one shown above, the Lyman Electronic 1000 grain scale. An ounce weighs 437.5 grains. Most loads are not going to exceed two ounces (875 grains) plus components.
Powder Charges Should Be Weighed
Powder should be weighed, especially when the grains are bulky, such as single-based
powders and the very slow-burning types. These don't flow as well as high speed powders
through bushings. Also, the bulk does not compact consistently, which means gaps
between the flakes can cause a lesser amount to be dropped. There is no way to
properly compact powder into a bushing, so your best alternative is to weigh the powder in
grains.
About Bushings and Accuracy
Fast burning powders, which drop accurately through bushings, are those you use for
lighter loads, up to 25 grains in the 12 gauge. An accurate and calibrated scale
should be used to verify even these loads, though, as a bushing size is merely a
representation of the actual grains it should be dropping.
Verifying the drops will remove all doubt concering interpretation.