well TBH range buff wouldnt help THAT much, the main thing it needs is doubled rate of fire (with coresponding halving of power cost and damage)
Prehaps boost the range to that of the cruiser torpedo turret, or a tad longer, as currently crusier torpedo turrets have a longer range.
Also if range is going to be increased, there should be a slight speed boost to the projectile, actualy a projectile speed boost would make aiming a tad easier and may fix the weapon.
But your right John range is too short on it, its the only seige gun in game, so the range should be the longest in game by a slight ammount.