Fire round corners?
They don't exaclty fire round corners, they just use the flatline barrel principle where one side of the barrel bore is a bit rough, hence putting a bit if spin on the paintball, hence allowing it to curve slightly.
On flatlines the top of the barrel is rough giving the paint a bit of backspin, hence why they have the distance, but apex barrels can be clicked round to the left, right, or even down, to curve the ball in the relevant direction. Note it is a slight curve, and not exactly 'shooting round corners'.
Hope useful info.