The chief pilot reported that the helicopter pilot told him that, while attempting to net a calf during a caribou capture flight, he got within shooting range for the net gun, but the calf suddenly "broke right." He then turned the helicopter to follow the calf, and while turning, the pilot thought the shot would not be possible and that he should set up for another run, but the gunner fired. The pilot heard a "bang," followed by a strong vibration. The pilot landed the helicopter without further incident. The pilot reported that postaccident examination revealed that one of the main rotor blades had sustained substantial damage, which he assumed was from a net weight. The chief pilot reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation.