In the briefing a picture of the sniper rifle used to kill the Chief Petty Officer and her husband is shown, with its specs listed below. It identifies the rifles caliber as a .338 Lapua Magnum, then below says that its NATO caliber designation is 7.62 mm. A bullet that is a 7.62 mm is .30 caliber, the sniper rifle in question fires .338 caliber bullets, so its NATO designation would be 8.58 mm, (full NATO designation for a .338 is 8.6×70 mm).
Abby states that the sniper has acquired a transceiver to find the frequency used by the target airport. This is unnecessary, the frequencies used by all airports, ground control (handles airplanes on the ground taxiing between the runway and ramps), "tower" (which handles airplanes that are landing or taking off) and navigation are freely available to anyone form any number of sources. All you need to listen in is a radio that can receive VHF signals. These radios can't transmit, but they are cheap and easy to get from any electronics dealer. There would be no reason Abby would know the sniper got a radio that could listen to air traffic.
The airport shown in the picture has only one runway, yet as the plane lands the radio chatter mentions Runway 22L. L,R, or C (center) are only used at airports with more than one runway going in the same direction (runways are numbered based on the heading an aircraft flies when using that runway). An airport with one runway would only have a number, not a letter.
Gibbs' finger position on the trigger of his rifle changes multiple times. A highly trained sharpshooter, particularly a sniper, is trained to be consistent in every shot so as to take most accurate shot possible. Small changes to hand and finger position alter the shot, and this especially effects long range shots.