First of all, I can't stress enough how important it is to destroy/hack all turrets on Tech Plants and Amp Stations. If you leave them alone for whatever reason, they will be used against you. Second, you don't have to be even near those turrets to take them out. Other turrets, Daltons, Sarons and AV turrets can destroy pretty much everything you need from great distance (especially when your target is standing still). For those who haven't tried it yet with the engineer's AV turret, it's even easier than with the other methods. The bullet drop is zero and I haven't seen any damage loss over distance. Since your aim will even go slightly up when shooting, they only thing you'll have to do is aim slightly under the turret and fire. After that, just keep your mouse still. It takes about 5 shots to down a turret. Hvar under siege: I've done the same from the rooftop of Sandstone Gulch to shoot the row at the other side of the building.
