A soldier is given the command to load, aim and fire, repeatedly and or at the fire-at-will command. Sometime during this repeated cycle the process is interrupted by events on the field, especially in a heavy fire-fight. A soldier is given another command to move position or halt fire and then resume firing. It would be very easy to have forgotten that a load was already in the weapon if the act of loading the primer was interrupted [the last stage of loading], which usually is an indicator the weapon is loaded. This has happened to me, with a very noticable report or more embarrassing misfire because I thought the weapon was loaded!
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David Upton