Snipers at Altitude

Discussion in 'Infantry' started by Jimima_Shark, Aug 6, 2006.

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  1. Interesting question for you snipers out there (well for me anyway)

    I have been following two threads with interest. Firstly the thread about snipers in Afghanistan and the problems that helicopters have at altitiude and temperature.

    Now I am aware that when taking a shot that wind, trajectory and fall of shot need to be taken into account.

    Is there an extra factor when taking a shot at altitude that needs to be considered as this affects the air through which the bullet will travel and hence it's motion?

    Cheers in advance

    Jimima
     
  2. Trajectory is flatter at altitude due to the air being thinner. There is a similiar effect in arctic regions due to the low relative humidity, and the opposite is true in the tropics where humidity is high.
    Air, its tricky stuff!
     
  3. Shooting "up" or "down" - eg in mountainous terrain - requires adjustment due to the different ballistic curves involved. Shooting "up" requires the elevation setting to be reduced - eg maybe 450m setting for a 600m target which is 50m higher than the shooter. Shooting "down" requires the elevation setting to be greater than the actual range. Don't know what the boys in Afghanistan are doing, but normally you need to zero "up" and "down",as well as normal elevation, to make a little adjustment table for the particular rifle/ammo.
     
  4. not to mention the amount of fish tailing wind that will be about the valleys. its bad enough on a range never mind the pressure of a shot. alot of practise and a good shooting record books helps. also the target standing still next next to a flag helps loads!!
     
  5. The opposite, surely?
     
  6. Drop cannot be anything other than exactly the same as when firing that gun on the level. The distance from muzzle to target is still 100 metres. The velocity of the round is still exactly the same, so that time of flight to the target is exactly the same. The acceleration of gravity is certainly always the same, since it is a physical and mathematical constant. A round free to fall, subjected to the acceleration of gravity for the same time, will fall the same amount. Drop is the same. The problem with conceptualizing it is in realizing the problem is the angle at which the drop occurs, not the amount of drop.

    The same error occurs in shooting down an identical slope, and to the same degree. All weapons shoot high when fired either up or down a steep slope.
     
  7. There are ready calculators available but you need to know what angle you are shooting at to use them. There are attachments available commercially that fit on the side of the scope that give an angle read out.
    The adjustments to make are as follows

    5 degrees = .99 of the lasered range
    10 = .98
    15 = .97
    20 = .94
    25 = .91
    30 = .87
    35 = .82
    40 = .77
    50 = .64
    55 = .57
    60 = .50
    65= .42
    70 = .34
    75 =.26
    80 = .17
    85 = .09
    90 = 0

    As an example:
    If you have a laser range finder and it shows a range of 600m and you are shooting up wards (or downwards) at an angle of 40 degrees then the setting on the scope will be for a range of 462m ie 600 x .77.

    The reason for the adjustments is that if you imagine the target as being part of a triangle with the target at the highest point then the lasered range is the hypotenus of the triangle which is the longest side. The horizontal side equates to the actual range for the effect of gravity and this horizontal distance is always shorter. A bit difficult to show without a sketch, if you need one PM me.

    There are probably sets of tables for altitude adjustment but as I have not had need to use them I haven't searched for them. A search on US reloading sites would give more info on this.
     
  8. Oooh, Mr. Picky. :roll: So remind me, why do we pass "altitude" back to the gun line on a fire mission?

    Try aiming straight up (the "Darwin Gun") or straight down. In both cases, there will be no curve to the trajectory, as gravity will be acting along the bullet's path. So, aiming will have to be adjusted to take account of the differences in elevation (which is the point of the question). In between vertical and horizontal, the effect will vary.

    It might be fair to say that the differences in aim required by different elevations is insignificant compared to typical errors in range estimation, or insignificant at a typical "battle range" of 300m.

    But if you're going for a long-range shot, into/out of a valley at a steep angle (oooh, aiming at vehicles from a hilltop with an L115 say), and you've got a laser rangefinder, then I can see it making a difference.
     
  9. Wrong, it does not matter if you're shooting up, or down,
    My instructors have explained it as having to do with the fact that if the bullet travels either up or down, the distance it travels under the effect of gravity is less than if both you and the target were on the same level plane. The tables like the one posted by RSupwood are what you can use. But the truth is, unless you're well beyond, say 600 meters, or shooting at an extreme angle the differences are too small to matter (esp. when you count in the problem of judging distances, whether with your eye, your optics or laser).

    Part 2:
    Altitude by itself does also matter, because air is thinner at heights, but that's something one needs to factor in right at the beginning of your exercise or mission (if possible), calculate while taking the shot (if possible) or just use a guesstimate (likeliest).

    (Sorry, this is my first posting).
     
  10. The Slope Doper is a handy little gizmo to help you dial in the correct correction factor.

    [​IMG]
     
  11. Whats even more worrying is a Crab with a machine gun.

    BT
     
  12. The velocity, trajectory and stability of the round are all affected by are density. The less dense the air, the less yaw, precession and nutation to the round theoretically giving greater accuracy. Throw in the other factors previously mentioned though such as wind sheer in valleys etc, the physilogical effect of thinner air on the breathing of a sniper and it probably pretty much balances out.

    The good news is once the round strikes anything denser than the thin air (And lets face it anyone who believes in virgins in paradise has got to be pretty dense) The round will destabilise and tumble quiet nicely in the body transfering most of it's energy into the wound.

    Bad news for anyone on the receiving end.
     
  13. Wow, what a great thread... perfect to pull balistics geeks out of the woodwork... to get more and more pedantic... love it!

    Yeps, air is thiner and thus air resistance is less and since this is proportional to the velocity squared, it'll have the effect of disproportionally streching the balistic trajectory out...

    But the temperatures tend to be less and thus the round will be colder before fired and thus the muzzle velocity less, thus reducing the range...

    But if that wasn't enough then the wind will be greater, causing more drift... but also increasing the gyroscopic magnus lift or depression (... which has already been affected by the reduced spin degradation... refer to point 1)

    And of course when it's colder the barrel will be thinner, causing more stiction in the chamber and more breech pressure (initially)...

    And... can anyone get more pedantic... :D or shall we just use automatic weapons?
     
  14. Call in an A-10
     
  15. Use all the automatic weapons that you want but if you do not allow for differences in height you will shoot over your target and the samller the target the more the error.

    Personally it's crows and rabbits at 200 to 300 yards and they don't shoot back.

    Man shaped targets do. :D