[Borodog]

Many guns have both single and double action. In double action, pulling the trigger both raises the hammer and fires. In single action, the hammer is already cocked, and pulling the trigger simply drops it, firing the weapon. Manually cocking the gun to single action means far less pressure s required to fire the gun than in double action. On a semi-auto that is initially uncocked, the recycle from the first round leaves the hammer cocked for subsequent rounds, meaning the the first trigger pull is "heavy" while subsequent pulls will be "light".