Which tests must be conducted after modifying a rifle's trigger?

When a rifle's trigger has been modified, conducting a drop test is essential because it ensures safety and reliability. A drop test checks whether the modified trigger will safely release the firing pin when the rifle is dropped or jolted. This is critical as modifications can inadvertently affect the trigger's disengagement mechanism, leading to unsafe conditions where the rifle may fire unintentionally.

Accuracy tests, while important for assessing the performance of the rifle after modifications, do not inherently address safety issues related to the trigger modification. Similarly, cleaning and lubricating the action and inspecting the barrel are routine maintenance tasks and do not specifically evaluate the impact of the trigger modification on the rifle's function or safety. Hence, the drop test stands out as the necessary evaluation to ensure that the firearm operates safely under all conditions after trigger modifications.