What is the maximum range of sniper?

http://xcom.wikia.com/wiki/Sniper_Class
One of the benefit of Squadsight is that you can shoot very far away as long as one of your team sees the enemy.
The catch is you need to have the line of sight.
Well, if I need to have the line of sight anyway, and if the sniper need to be able to "see" the enemies, what's the point of squad sight then?
I do notice that squadsight snipper tend to shoot far away.
So is there a range limit for sniper?
My take is the weapon itself has no limit but the sniper itself have limited vision range.
Am I correct? If so what's the range?
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Which Gun Has Longest range?
The famous long-range gun that shelled Paris, France in World War I was the Paris-Geschütz  'Paris Gun', with a calibre of 21 cm (8.26 in), a designed range of 127.9 km (79.4 miles) and an achieved range of 122 km (75.8 miles) from the woods of Crepy in March 1918.What is the range of a sniper scope?
A sniper can adjust for any range up to 1,000 yards, as well as make adjustments up, down, left or right.New long range shooting record - 3720 yards
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