Sniper Rifle

Description
If you can see your long distance enemy in a straight line then this is the best weapon to use. Even though you can have a couple of efforts with the Shotgun, the Sniper Rifle offers a far higher level of accuracy with its zoom feature.

When in First Person view it is easier to zoom as far as you can outwards, find roughly where your target is, then zoom inwards as far as you need to.