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Highly incorrect airFriction / ballistics values in 1.12 experimental
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Description

Multiple airFriction values were changed in 1.12 experimental and most are worse than the values in previous patch 1.11.

This affects the authenticity of rounds' time of flight, bullet drop, damage dropoff, relative characteristics, , etc and etc. Hopefully this can be corrected before stable release. I will describe some of the errors below:

5.45x39 has -0.00165.

This is way, way too high! The 5.45x39 is supposed to be MORE aerodynamic than the 7.62x39. In 1.12 it's the opposite! In fact it's so high M4 still kills in two shots at a range where AK-74 takes 5 shots!

With a 0.93 form factor, the bullets should have airFriction of:

-0.00118 (7N6 round, 900 m/s)
-0.00113 (7N10 round, 900 m/s)

7.62x39 has -0.00135

This is actually not that bad. But it's not an improvement on the old -0.00143. You should change it back as the former value was IMO more accurate. Depending on the source the steel-core FMJ should have something in the range of -0.00137 to -0.00146. So the 1.11 value was great.

-0.00143 (7.9 g steel core ball, 715 m/s)

5.56x45 has -0.00095

This is way too low! It's lower than ARMA 3 value for .308 ball. The 5.56x45 ball ammo is not as aerodynamic as the 5.45x39.

It should have about -0.00126 for the standard 62 grain steel core "green tip" (the 55 grain M193 on the other hand should have about -0.00156, however this is not a standard load among Western armies and initSpeed/typicalSpeed does not match this load).

-0.00126 (SS109 ball, 900 m/s, 16" barrel)
-0.00156 (M193 ball, 945 m/s, 16" barrel)

308 Winchester has -0.00045

Waaaaaaaaaaaaaaay too low! It's lower than even the airFriction for .408 CheyTac in ARMA 3 (which is -0.00048, and that is an accurate value). I don't know how this value was arrived at.

This means the .308 has 75% longer killing range than 7.62x54R, despite being extremely similar rounds especially in military configuration. With ball rounds they have energy, velocity, calibre, weight, ballistics practically the same. The .308 is slightly more powerful and the 7.62x54R is slightly more aerodynamic.

Authentic values:
-0.00101 (M80 ball round, 853 m/s, 22" barrel)
-0.00085 (Mk 316 Mod 0 sniper round, 805 m/s, 24" barrel)

7.62x54R has -0.0007

Again, it's much too low. The typical steel core ball has a ballistic coefficient only slightly higher than .308 M80. Realistic values:

-0.00097 (steel core light ball, SVD, 835 m/s)
-0.00095 (7N1 sniper round, SVD, 830 m/s)

Compared to a match round:

-0.00082 (200 grain Extra match, 750 m/s)

45 ACP has -0.00195

It's way too high! The .45 ACP should have a low airFriction because it is a subsonic round, meaning that even though it's not very aerodynamic, it experiences a lower drag force. See figures from McCoy, Winchester, Federal, Hornady. The .45 ACP should have an airFriction like:

-0.00082 (230 grain ball, 259 m/s)

9x19mm has -0.001

And this is much too low! The 9mm starts off at transonic speeds, right near the sound barrier. This means it experiences a very high drag force right away. The airFriction should be about double this, more like:

-0.002 (124 grain ball, 350 m/s)

380 ACP has -0.0025

This is much too high! It's the reverse of the 9mm now. The .380 is a subsonic cartridge, so it doesn't experience a high drag force. However it is not aerodynamic. It should be about:

-0.0016 (95 gr ball, 290 m/s)

22 LR has -0.005

Way too high, the previous values in pre-0.62 DayZ were closer. The .22 LR 40 grain bullets at 1200+ muzzle velocity have a ballistic coefficient of about 0.130 G1, which means an airFriction of about:

-0.0026 (40 gr CCI Mini-Mag, 376 m/s)

357 Magnum has -0.0014

It should be higher, similar to 9mm the .357 Magnum passes through the transonic barrier shortly after being fired and experiences a high drag.

The problem is there are two sets of ballistics because the .357 Repeater has such an increased muzzle velocity. A compromise airFriction could be set. Authentic airFrictions:

-0.0024 (158 gr soft point, 376 m/s, revolver)
-0.0030 (158 gr soft point, 558 m/s, rifle)
-0.00285 (compromise value 442 m/s)

9x39mm has -0.00055

It's good it's pretty low, but it should be lower. The bullets are designed specifically for subsonic flight, they experience low drag due to subsonic speeds and unlike a .45 ACP they are aerodynamic. Ballistic coefficient can only be estimated, but airFriction should be about:

-0.00035 (9x39 SP5, SP6, 290 m/s)

12 gauge pellets have -0.00575

It should be even a little bit higher, it should be about -0.008 at averaged over 50 m range. See drag coefficient of sphere. Also could be 9 pellets instead of current 8, as 9-pellet 00 is the most standard buckshot load.

-0.008 (00 pellet, 400 m/s)

12 gauge slug has -0.005

And no complaints, it's correct in velocity and airFriction for a Brenneke-type slug.

Details

Severity
Tweak
Resolution
Open
Reproducibility
N/A
Operating System
Windows 10 x64
Category
General

Event Timeline

Gews created this task.Apr 10 2021, 1:52 AM
Beavis added a subscriber: Beavis.Apr 10 2021, 3:03 PM

Thank you Gews for posting this, I dearly hope the devs listen!

WOBO is that you?

Masgel added a subscriber: Masgel.Apr 12 2021, 4:09 PM

This needs more attention...and discussion with the devs.

Geez changed the task status from New to Assigned.Apr 14 2021, 2:26 PM
Geez added a subscriber: Geez.

Hello everyone.

There have been deliberate changes to these values, however, they are not final and are still subjects to tweaking and balancing.

Regards,
Geez

Gews added a comment.Wed, Apr 21, 5:42 PM

Hi @Geez with recent changes to 1.12 there seems to have been a typo where 7.62x54 (Mosin, SVD) airFriction now has -0.0001, this was probably supposed to be -0.001.

-0.0001 = over 5 kilometres one-shot kill (G7 ballistic coefficient ~1.9)
-0.001 = ~550 m one-shot kill (G7 ballistic coefficient ~0.2)

for comparison
in 1.11 it's ~500 m one-shot kill
in early 1.12 exp it's ~400 m one-shot kill

I don’t know anything about ballistics, but I think if you go to the trouble of having a nuanced bullet drop system, it makes for it to be as realistic as possible.