Barrel Shot(バレルショットBareru Shotto) is a composite high-speed bombardment spell with supportive effects cast by Nanoha Takamachi. It is a prerequisite for casting other, extremely powerful bombardments, as it assists sighting, stablizing the bombardment route, and controlling the energy diffusion.
When cast, an invisible Bind-type spell is shot at the opponent, preventing their movement and leaving them open for a bombardment attack. It is extremely useful for mages utilizing guerrilla tactics, and can also be used in mid-range high-speed battles.
It is not the similar shockwave sent from Bardiche to the Defense Program of the Book of Darkness when Fate casts Jet Zanber in A's episode 12. That shockwave is for physical destruction purpose.