Bullet trajectories

[-Gews- 7443]

Edit: can someone move this to "DayZ General Discussion" please and thank you?

 

This is just one of those "I am bored" theoretical threads which has no real practical purpose.

Anyways, I wanted to investigate bullet trajectories more after reading this thread on elevation vs trajectory and playing a bit of Takistan Wasteland. At normal ranges it seemed like elevation had little effect in-game, but at extreme ranges shooting down or uphill can have a very large and noticeable effect.

 

The other most frequently comment I've seen is that old chestnut "the Lee-Enfield has no bullet drop"... which is of course nonsense...

 

 

 

Anyways after seeking online help and getting my poor trigonometry skills sorted I was able to calculate (theoretical) time of flight, (theoretical) bullet drop and (theoretical) deviation from line of sight for different weapons.

 

 

 

This is just one of those theoretical threads which has no real practical purpose.

Anyways I wanted to investigate bullet trajectories more after reading this thread and playing a bit of Wasteland.



Trajectories (meters):


FN FAL

200 = +0.2 meters
300 = ZERO
400 = -0.5 meters
600 = -2.5 meters



Lee-Enfield

200 = +0.3 meters
300 = ZERO
400 = -0.6 meters
600 = -3.1 meters
 

 

AK-74

200 = +0.2 meters
300 = ZERO
400 = -0.6 meters
600 = -3.8 meters

 

Winchester 1866

Drop at 50 = ZERO
Drop at 100 = -0.3 meters
Drop at 150 = -1.3 meters
Drop at 200 = -3.4 meters
 

 

M16A2

Drop at 200 = + 0.2 Meters
Drop at 300 = ZERO
Drop at 400 = - 0.6 meters

 

M24 (zeroed at 800 meters)

Drop at 800 = ZERO
Drop at 1000 = 5.9 meters
Drop at 1375 = 33.1 meters

 

SVD

Drop at 200 = ZERO
Drop at 700 = 5.4 meters
Drop at 1200 = 31.5 meters

 

 

 

 

So the Winchester has roughly the same drop at 200 meters as an Enfield / AK at 600... pretty bad although that's not exactly news to anyone.

 

 

 

I was more interested in the drop of the SVD and M24 at long range. When I calculated it they both dropped over 30 meters from the line of sight. However, when looking at screenshots, the drop appears to only be about 20-25 meters (judging by crouching 1.5 meter figure).

 

SVD, 1196 meters before moment of firing

 

M24, 1373 meters before moment of firing

 

 

 

In the photo above a drop of 33 meters certainly seems wrong. So...

 

 

My calculations were made assuming a gravitational constant of -9.81 m/s^2.

 

However, I read comments saying ArmA used something rather less than that, closer to -7.5 m/s^2. I also read comments saying it used different gravitational constants for different simulations.

 

 

 

 

When I run calculations using the -7.5 m/s^2 figure, I get a drop of almost exactly 25 meters with an 800 meter zero and a range of 1375 meters. That seems much closer to what I see on screen.

 

However, the numbers are still useful when considered relative to each other - they should be proportionally correct....

 

In any case this warrants further investigation...

Edited September 5, 2013 by Gews

[Statik (DayZ) 2695]

Gews, y u so smart?

[-Gews- 7443]

Gews, y u so smart?

 

I'm not, I just wonder about stuff, much like the monkey in the picture below :P

 

 

Anyways I wanted to test it out immediately, so I set up a target at 1,375 meters. This target is just a series of 1x1 meter blocks, by aiming at a specific block, eliminating dispersion and using a bullet cam script I can see where the bullet impacts and determine the drop to the nearest meter or so.

 

 

Observed drop for M24 @ 1375 was about 21 meters.

Observed drop for Lee-Enfield @ 600 was about 2.3 meters.

Observed drop for Lee-Enfield @1000 was about 12 meters.

 

 

 

Results of calculation using g = -7.35 m/s^2

 

 

Calculated drop for M24 @ 1375 was 24.5 meters

Calculated drop for Lee-Enfield @ 600 was 2.2 meters

Calculated drop for Lee-Enfield @ 1000 was 11.5 meters

 

 

 

 

 

 

Next step is spawning objects in air and recording their velocity as they hit the ground; from there determining BIS gravitational constant.

[Korsbaek 1778]

This is awesome! How do you find the time for this?

[Jex 1104]

Why does the Lee Enfield have under half the trajectory of the M24 - is it a larger round? Can I put a scope on the Enfield - wouldn't that be the best sniper rifle out there? lol

[-Gews- 7443]

Did some more work on this problem. From testing in-game, I found my calculations using g (-9.81 m/s^2) and 0.75*g (-7.35 m/s^2) worked okay at short and medium range. However, when stretching the distance to nearly 1600 meters the calculations started giving very poor results.

After experimenting some more I observed the following drop from the M24 in-game:

1000m: 4-4.5 meters

1400m: 23-24 meters

1550m: 36-37 meters

I tried calculations using (2/3)g as the gravitational constant and got the following calculated results:

1000m: 3.95

1400m: 23.7

1550m: 38.1

Therefore I am now working under the assumption that BIS uses (2/3)g for bullets.

This is awesome! How do you find the time for this?

I should really be doing other things.

Why does the Lee Enfield have under half the trajectory of the M24 - is it a larger round? Can I put a scope on the Enfield - wouldn't that be the best sniper rifle out there? lol

The drops are at different ranges and with different zeroing for each. Comparing the Lee-Enfield with the FN FAL gives a better picture (FN FAL has same ammunition and speed as M24):

FN FAL trajectory:

300 meters: ZERO

400 meters: -0.3 meters

500 meters: -1.0 meters

600 meters: -1.9 meters

Lee-Enfield trajectory:

300 meters: ZERO

400 meters: -0.4 meters

500 meters: -1.1 meters

600 meters: -2.2 meters

Speaking of Lee-Enfield trajectory, here is a fun problem:

1500-1600m... With a Lee Enfield... To a chopper pilot... Probably in the head... Yeah...

It only took a few mags.

So, how far would deejay2900 have had to aim above the chopper to pull that off at 1500 meters?

Zero range = 300 meters

Time of flight = 3.59 seconds

Total drop = 47.7 meters

So that means deejay2900 would have had to aim at a point approximately 43.9 meters above the pilot (144 feet) with a final damage of 2,300.

Another example: xxnickpwnsxx posted a video of a 1675 meter shot with a KSVK. How far above his target did he have to hold?

Zero range = 200 meters

Time of flight = 3.25 seconds

Total drop = 39.1 meters

Therefore xxnickpwnsxx would have had to aim at a point approximately 37.1 meters high (122 feet) with a final damage of 19,850.

[-Gews- 7443]

Update, the drop at various ranges can be converted into holdover in mils. However, when I tried the calculations I realized something was off, since the calculated holdover did not match what I knew to be true in game - either the calculations or the mil dots were wrong. Liking my calculations so far, I hoped it was the dots.

 

I made a target with various sizes of squares (1.6m, 1.7m, 1.8m, 2.0m, and 8.0m) to check if the mil dots were properly calibrated. I found they were not.

 

At 300 meters one mil should subtend 0.3 meters. By taking screenshots and measuring at different ranges, I found the space between the dots only appeared to subtend about 0.276-0.277 meters at 300 meters (or 0.920-0.923 mils). The effects of this error became even more pronounced at long ranges, at 1000 meters a target that should have been 8.00 "mils" high actually appeared 8.69 mils high, quite a large error, and one that would induce a rangefinding error of EIGHTY meters.

 

This means the range-finding formula for standing human targets (size in meters x 1000 / size in mils) will give increasingly incorrect results at longer ranges.

 

 

[dulix11 731]

You have a lot of time on your hands, Gews.

[Heiduk 265]

I don't remember which one it is off the top of my head, but one of the target range mods/missions allows you to export bullet trajectories so you can analyze them in a spreadsheet. It may even allow you to make plots of the trajectory while you are in the mission, but it has been a while since I played around with it.

[-Gews- 7443]

I don't remember which one it is off the top of my head, but one of the target range mods/missions allows you to export bullet trajectories so you can analyze them in a spreadsheet. It may even allow you to make plots of the trajectory while you are in the mission, but it has been a while since I played around with it.

 

I use them for confirming (or disproving) things.

 

However for actual calculations: