http://www.theregister.co.uk/2010/05/25/darpa_terry_pratchett_gunsights/US military boffins are about to produce a field-ready computer gunsight which will let snipers kill people on their first shot from a mile away - even with troublesome winds blowing.
The technical issues facing the so-called "One Shot" project have already been solved using prototype equipment, and it is now planned to produce 15 "fully operational and field hardened" sets of gear for further development trials on the battlefield.
Modern-day sniper rifles can easily throw their bullets across tremendously long distances, but beyond a certain point it becomes impossibly difficult to adjust the aim to allow for atmospheric effects - in particular for the wind. It can also be a time-consuming business allowing for all the changing factors which can affect the path of a bullet's flight - range, temperature, atmospheric pressure, the spin of the projectile itself, the relative heights of the target and shooter.
Thus it is that very long-range hits beyond 2km do get made, but they are rarities. The current combat sniping record is nowadays generally credited to Corporal of Horse Craig Harrison of the British Army, who hit and killed two Taliban machine-gunners at a distance of 2,474 metres in November last year in as many shots - and then destroyed their weapon with a third round.
Harrison was able to make these astonishing shots, however, because - in his words - "conditions were perfect, no wind, mild weather, clear visibility".
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But in general, even powerful sniper rifles like Harrison's L115A3 Long Range Rifle (aka the Arctic Warfare Super Magnum** from Accuracy International) aren't expected to achieve a first-shot kill further off than 600m, and "harassing fire" to 1100m. In particular, the estimation of crosswinds between the shooter and the target is usually a matter of educated guesswork. Then, making the right corrections for range, height, bullet spin, temperature, air pressure etc can take so long that the target has moved away before the sniper can shoot.
But it seems that there's no need for this to be the case. US military trials have found that a laser beam shone on the target can do more than just determine the range: it can also be used to "measure the average down range crosswind profile". The laser information can be combined with automatic readings of temperature, humidity etc and a "ballistic solution" computed.
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