Homing Projectile support gem

Radius
At the end of a projectile's range, it will find an enemy within a 120 degree arc in front of itself and fly towards them. If no valid targets are within this radius, the projectile parishes at maximum range.

Maximum Range
Projectile Speed normally does not affect the total distance a projectile can travel, unless it has a duration like Freezing Pulse or Ethereal Knives. For other projectiles, they have a maximum range of 120 units, or in colloquial terms one-and-a-half screens away. Because the camera is skewed at an angle looking down at your character, the distance to the top, bottom, and sides of the screen are different. To the bottom of the screen is only 50 units, to the top is ~70 units, and to either side is 85 units.

Less Projectile Range
From 120 units, it would be cut down to 48 units. For projectiles that use a duration instead, Less Range applies to its duration. This reduction to duration only applies to its travel life, and not to any other effects that have a duration.

Lesser/Greater Multiple Projectiles

Faster/Slower Projectiles

Fork, Chain
A projectile that does not hit anything will seek out a target, and on hit will fork or chain normally. Homing Projectile only concerns a projectile that has reached maximum range, and does nothing more after the primary projectile has hit.

Pierce
Regardless if a projectile has pierced, so long as it reaches its maximum range it will still seek. If it pierces the target it homed in on, it will continue to fly to the maximum range of its seek radius and can continue to pierce.