"A very high velocity variant of the gauss cannon that uses a nano-rifled barrel to create a very long range very accurate at long distances gauss weapon. The speed of the shot and slow barrel tracking makes the weapon less useful at close ranges though."
The Sniper Cannon tech node is an early dead end in the Ballistic Weapons tech tree which costs as much as 22,500 or as little as 7,500 research points to complete depending on chance. It unlocks the Sniper Cannons(weapon) for use in small mounts.

Root Technologies
And/Or Technology Research Cost Chance to unlock Sniper Cannons
Human Hiver Liir Morrigi Tarka Zuul
And Gauss Driver 0 70 90 50 40 85 60
Fission 0 0 0 0 0 0 0

Legacy Wiki, this page does not distinguish between the technology and the weapon.