Recently after watching the latest regional competitions I've seen players using HLC in the 360 arc. Why does the firing arc not apply to the 2400?

Outrider title.

Outrider
YT-2400 Freighter Expansion Pack

YT-2400 only.

While you have a (Cannon) Upgrade card equipped, you cannot perform primary weapon attacks and you may perform (Cannon) secondary weapon attacks against ships outside your firing arc.

On 4/20/2018 at 11:51 PM, Mdburg23 said:

Recently after watching the latest regional competitions I've seen players using HLC in the 360 arc.

There is no 360 arc... it just shoot outside of arc

Yup! A title exclusive to the YT-2400, that allows it to perform cannon attacks like a turret, at the cost of its ability to perform regular primary attacks:

A nice side note to the Outrider title: It only prevents the primary weapon from being used to attack, not any other secondary weapons. So secondary weapons like Snap Shot and the missiles can still be used if the target is in arc. The "donut hole" that comes with the Heavy Laser Cannon typical build can be partially filled this way, by using Snap Shot, Cluster Missiles or Proton Rockets.