What is a possible effect of a cartridge filled with too little powder?

A cartridge filled with too little powder can lead to weak and uneven powder burn due to insufficient pressure being generated within the cartridge. When there isn’t enough propellant, the combustion process may not be complete or may not produce a consistent flame front. This inconsistency results in reduced chamber pressure, which can affect the projectile’s velocity and overall performance.

In contrast, the other options suggest outcomes that are typically associated with adequate propellant levels. Increased muzzle velocity typically occurs with optimal or higher powder charges, while cleaner combustion is more likely achieved with proper powder load that allows for efficient burning. More reliable cycling is generally related to the cartridge's ability to generate adequate pressure to cycle semi-automatic actions effectively, which would also be compromised by an insufficient powder load. Thus, the primary effect of having too little powder is the risk of weak and erratic performance during firing.