Kalezian said:
I think I talk for a lot of FPS gamers out here, if the FPS you are playing has killstreak airstrikes [CoD or Homefront] it IS noobish and generally trashy to use something like a carpet bomb, Cluster Bomb, or artillery to kill ONE PERSON.
Pisses me off to no end.
It's oh, so very useful for camping snipers, though, and if you do it just right you can broadcast "Hey, sniper, catch!" quarter of a second before the first bomb drops right on his helmet.
As for snipers, this guy:
... should have missed.
Rifle muzzle velocities tend to be in the 800-1000m/s range, and velocity drops off with range, which is why the 7.62x39mm can be more powerful than the 5.56x45mm at the muzzle but have less energy at 300m: it's a shorter, fatter bullet slowing down more quickly.
If we ignore the slow-down completely because I can't be bothered looking up the numbers, and go with a simple number like 1000 metres per second even though that's rather faster than pretty much anything (L86 gets close with 970 but the .50 is apparently nearer 850 unless you use saboted sub-calibre rounds) we get very simple time-to-range figures:
10m: 0.01s
100m: 0.1s
200m: 0.2s
300m: 0.3s
400m: 0.4s
et cetera.
If the target's strolling, he's doing 1.5m/s. Walking fast, 2m/s. Running in a crouch with heavy kit on, 3m/s. Competing in the Olympics and approaching the finish line of the 100m sprint, 10m/s. Let's take a running man, weighed down by kit but boosted by adrenaline, as doing 5m/s. This combines with the numbers above to give us how far in front of him you have to aim:
10m: 5cm
100m: 50cm
200m: 1m
300m: 1.5m
400m: 2m
500m: 2.5m
et cetera.
Distance fallen is (0.5)(a)(t^2) and we'll just call gravity 10 metres per square second ... "square second"? ... for simplicity so the distance your bullet has fallen below the level of a horizontal barrel at range is:
10m: 0.5mm
100m: 5cm
200m: 20cm
300m: 45cm
400m: 80cm <=== quarter of a mile away, it's fallen three feet two inches.
500m: 1.25m
600m: 1.80m <=== at the official effective range of the SA80 as a section weapon, it's fallen six feet.
700m: 2.45m
800m: 3.2m <=== half a mile away, ten foot six down.
900m: 4.05m
1km: 5m
1.5km: 11.25m
2km: 20m
2.5km: 31.25m <=== Longest recorded sniper kill isn't quite this far.
Of course, you're not aiming through the gun barrel. You aim through sights mounted above it, or beside it in some cases. With range adjusters and so on quite where you're looking can change, but let's simplify it and assume you're looking through a point 5cm above the muzzle at the centre of your 200m group, i.e. your sights are zeroed at 200m.
How far below the line of your barrel you're looking:
10m: -3cm <=== you're looking above your barrel.
100m: 7.5cm
200m: 20cm
300m: 32.5cm
400m: 45cm
500m: 57.5cm
600m: 70cm
700m: 82.5cm
800m: 95cm
900m: 107.5cm
1km: 120cm
1.5km: 182.5cm
2km: 245cm
2.5km: 307.5cm
How far below your line of sight the bullet goes:
10m: 3.05cm
100m: -2.5cm
200m: 0cm
300m: 12.5cm
400m: 35cm
500m: 67.5cm
600m: 110cm
700m: 157.5cm
800m: 225cm
900m: 297.5cm
1km: 380cm
1.5km: 942.5cm
2km: 1755cm
2.5km: 2817.5cm
All in all, I think that gives us a picture something like this:
[http://imageshack.us/photo/my-images/228/ballistics4.jpg/]
The blue grid and red crosshairs show where your barrel has to be pointing at each distance, and the green lines show where you have to be aiming.
It looks suspiciously neat how the green lines skim under the red crosshairs like that, but that's how I worked it out just now. Maybe I used the wrong numbers or something.
Still, the principle's sound. Assuming zero air resistance, shooting at that running soldier at those ranges, you need to aim that sort of distance ahead of and above (or below) your desired impact point. The 3cm adjustment at 10m is really only for shooting off locks, putting a bullet in through an air vent or view slit, taking someone's trigger finger off at the knuckle and that sort of showy stuff, not for normal combat shooting. The 400m adjustments are relevant, though, and not taken into account in that video. Aim right at the running man from that distance and he really does get dust kicking up behind his feet as he goes.
--
Before someone complains about me posting university physics courses, note:
I ignored air resistance.
I ignored wind effects.
I ignored angle of depression or elevation.
I ignored the coriolis effect.
Really, that's the simple version.
Edit because I got the sight-line wrong, so all the green points were off. Also extended range to 2500m for the boggle value.