Bug Report: F-15 gun accuracy does not match sources - ED Forums
 


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Old 12-17-2017, 06:11 PM   #1
Aries144
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Default Bug Report: F-15 gun accuracy does not match sources

Testing has revealed that the F-15's current gun spread in DCS is currently over 20 mil. All sources I can find indicate that the F-15's gun has a minimum accuracy of 8 mil, 80%. A new video has come to light which demonstrates that a new M61 actually shoots closer to 6-7 mil, 95%. I'm suggesting simply using 8 mil as the most accurate compromise, considering DCS' limitations in modeling dispersion.

Can we please get this fixed?

ETA:

I used the F-5 as a testbed, since it uses the same accuracy value in the shelltable and since it features a 40 mil gunsight which easily allows a dispersion pattern to be measured. Using only one gun, and with all rounds changed in the shelltable to be tracers, I found the following:

A continuous burst of all ammunition, fired from the right side gun only, produced an extreme spread measuring at least 20 mil.

In a subsequent test, intended to establish the relationship with the lua files da0 value and real world mil measurements, I found the following:

With the F-5's Da0 value set to 0.0040, and with a continuous burst of all ammunition in the right gun, it produced an extreme spread where individual rounds could be seen extending out to touch the outer ring of the 40 mil gunsight, indicating that the dispersion diameter/extreme spread was approximately 40 mil.


Pending more precise testing, it's a safe assumption at this point that using Da0 = 0.0008 instead of Da0 = 0.0022 would produce a result much closer to the source value of 8 mil.

As further evidence, this video at 4:15 shows an M61 20mm cannon accuracy test. Firing a 100 round burst at a range of 25.4 meters, all rounds can be seen to fit well inside the 8 mil circle on the target. The video goes on to comment at 4:30 that a burst was fired at another target at 304.8 meters and that 95-99% of rounds fell within the 8 mil circle on that target.

Tracks didn't work. Here's some raw video recorded with ShadowPlay instead.

Default accuracy, Da0 = 0.0022

40 mil accuracy, Da0 = 0.004

8 mil accuracy, Da0 = 0.0008

ETA:

New information incoming. I just discovered that it is possible to freeze the aircraft using active pause, decelerate time using alt z, and shoot the cannon in slow motion with no movement of the aircraft. This will make the next videos posted as accurate as if the aircraft were stationary on the ground!

Last edited by Aries144; 12-22-2017 at 11:17 PM.
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Old 12-17-2017, 06:39 PM   #2
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M61 super shotgun device, puts the Doom Slayer to shame
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Old 12-17-2017, 11:03 PM   #3
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IIRC the M61 should have an 8 mil dispersion at 1000 feet. So 90% of the bullets should pass through an 8 foot diameter circle at 1,000 feet.
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Old 12-17-2017, 11:10 PM   #4
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It's the same with the F-5E's guns, the Huey's miniguns, the GAU-8/A cannon...
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Old 12-17-2017, 11:24 PM   #5
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Quote:
Originally Posted by SinusoidDelta View Post
IIRC the M61 should have an 8 mil dispersion at 1000 feet. So 90% of the bullets should pass through an 8 foot diameter circle at 1,000 feet.
8 mil is an angular measurement, so "8 mil" is 80cm in diameter at 100 meters, 4 meters in diameter at 500 meters, 8 meters in diameter at 1000 meters, etc. 8 mil is always 8 mil, no matter what distance you measure it at.

It has a relationship with meters similar to how MOA relates to inches.

The M61 Vulcan cannon has an accuracy requirement of 8 mil, 80%. If more than 80% of fired rounds land outside of an 8 mil diameter circle during maintenance tests, repair is required.
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Old 12-18-2017, 12:57 AM   #6
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Quote:
Originally Posted by Aries144 View Post
8 mil is an angular measurement, so "8 mil" is 80cm in diameter at 100 meters, 4 meters in diameter at 500 meters, 8 meters in diameter at 1000 meters, etc. 8 mil is always 8 mil, no matter what distance you measure it at.

It has a relationship with meters similar to how MOA relates to inches.

The M61 Vulcan cannon has an accuracy requirement of 8 mil, 80%. If more than 80% of fired rounds land outside of an 8 mil diameter circle during maintenance tests, repair is required.
Yeah, I worded that poorly. Regardless it should be 8 mil dispersion 80% circle. A quick and dirty way is milliradians will equal the diameter of the circle (in feet) at 1000 feet almost exactly: Tan(.008 rad)*1000

How are you testing it in DCS? I’ve wondered how accurately it’s modeled but never tested.

Last edited by SinusoidDelta; 12-18-2017 at 01:01 AM.
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Old 12-18-2017, 01:02 AM   #7
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M-61 has free-floating barrels to increase the spread. Whether they're used in the F-15C and how they're trimmed is anyone's guess. I recall some study about a specific 14mil pattern being set up for the F-16 with the same gun, but I can't find it now :/
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Old 12-18-2017, 01:04 AM   #8
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A bit off topic but just my opinion if they were to fix something it would be the lag faced in MP. I would be willing to bet the missile and gun fixing of realism threads would go down 90%. I see probably 60-80% of peoples missiles missing due to lag.

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Old 12-18-2017, 01:14 AM   #9
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Yes, you're way off topic, and it has nothing to do with actual gun dispersion.

In any case, I'm also thinking that we're pretty much never testing the gun from a stationary aircraft and so, it is possible that the dispersion appears to be larger than it ought to be (ie. it doesn't fit correctly inside an imaginary 8 mil circle in the HuD).

Edit: According to what OP found in the LUA files, this would be an easy thing to test and fix.
Second Edit: Are there too many zeros in the OP's post for everything non-M61 in fact or is it a typo?
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Last edited by GGTharos; 12-18-2017 at 01:20 AM.
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Old 12-18-2017, 02:43 AM   #10
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I completely missed the bit about the lua file. My bad.

Milliradians should be .00X radians, right?
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