Complex sentence: Once in service, it quickly became apparent that the AVS was not a satisfactory design, the operating mechanism was overly complicated, and the problem was made worse by the rifle's construction which let dirt get inside the weapon.
Split into simpler sentences: Once in service, it quickly became apparent that AVS was not a satisfactory design. Operating mechanism was overly complicated, and the problem was made worse by rifle's construction which easily let dirt inside the weapon.