Powder
density. The manufacturer's tolerance can cause a slight variation
from the weight shown on the chart, and may even vary from lot
to lot.
Individual
operators give varying amounts of vibration to the machine causing
the powder to pack. All loads should be checked during the actual
reloading cycle. Do not just throw a powder charge and expect
it to be the same as during the reloading cycle. Even the amount
of powder in the reloader's bottle may cause a slight variance.
Powder
exposed to the atmosphere can pick up moisture and weigh heavy.
The
larger the flake size, the lighter the charge tends to be.
A
machine that is not solidly mounted will usually not throw charges
as uniform as one that is.
Single-stage
machines will usually throw heavier charges than progressive
reloading machines.