[CLOSED] M61 Dispersion

Hello Everyone,

I do not know what the big mystery is about this variable. It's clearly stated in the manufacturer's specifications from General Dynamics brochure.

https://www.gd-ots.com/wp-content/uploads/2017/11/M6A1A1-M61A2.pdf

Happy Simming,

Monnie

It's now labelled as "No bug", so no ED'ler will ever take note of any true input in this thread.

They haven't fixed this issue in the past years so why should they now change their mind?

Just because of R/L input?

I know! I mean come on... Somebody screwed up. 0.60 = 60%, 0.06 = 6%. I think the word "mil" got warped in translation. Even so, whatever was coded in the file is not working correctly. Even the 3 barrel gun for helicopters got corrected (with the same info!). The 1000 inch bore sight panel in the video shows good grouping. The 1000 foot target showed good and similar "conical" grouping within the 14 foot square target panel, and 8 foot circle bulls-eye. Remember, and this is true for the M2,M3 machine guns, an 8 foot "dispersion" at 1000 feet is fantastic! 1000 feet, that is 0.18 or so miles. 14 feet is less than the wingspan of a MiG-15. And how many western aircraft does this effect?

Was busy at work before I finally clicked post above...

Now, I will try to be diplomatic but this kind of thing really makes one question the possibility of bias. I got hammered like many noobs for griping about things before I fully understood them when I first joined. But then I also learned just how badly things had been fouled up by so-called fixes that were not thought out. This rhetorical deflection seems like a defense mechanism and an attempt to distract with smoke and mirrors from simple failings that would otherwise be so easy to fix. "Why?" is the natural question that follows. The empirical evidence and proof with language and photos in the YouTube video shows the code data does not work correctly and does not achieve the "8 mil" spoken of by General Dynamics staff. I recently found a bug in the MiG-19 g-suit detail. It got fixed fairly quickly. It was an obvious violation of the standard set forth in the very same entry in the lua. What is that other than bias?

And as far as gunnery errors go... Give us the chance to screw up wind and aim and over correction fair and square. We don't need these human errors programmed into every weapon! That's what the sim is for!

I know! I mean come on... Somebody screwed up. 0.60 = 60%, 0.06 = 6%. I think the word "mil" got warped in translation. Even so, whatever was coded in the file is not working correctly. Even the 3 barrel gun for helicopters got corrected (with the same info!). The 1000 inch bore sight panel in the video shows good grouping. The 1000 foot target showed good and similar "conical" grouping within the 14 foot square target panel, and 8 foot circle bulls-eye. Remember, and this is true for the M2,M3 machine guns, an 8 foot "dispersion" at 1000 feet is fantastic! 1000 feet, that is 0.18 or so miles. 14 feet is less than the wingspan of a MiG-15. And how many western aircraft does this effect?

Any vehicle that uses the M61 with this ammunition types:

M61_20_HE

M61_20_HE_INVIS

M61_20_AP

Which would mean

(F14 is made by Heatblur and uses the correct values)

F15

upcoming F16 will have it too

F/A-18

Close-in weapon system of every US ship

M167

M163 VADS

If there will ever be a ED developed Phantom or Thunderchief, these will also have the same issue.

Do you think this thing will by fixed on the Viper? Why or why not?

OMG! Please ED, you can do it! No one is perfect and everyone makes mistakes. If this gets fixed on the Viper et al., DCS will rock the summer! If not, I will buy another tank of gas for my Ferrari instead ;)

Do you think this thing will by fixed on the Viper? Why or why not?

It won't be fixed, as this issue seems to be known for serveral years. Even though the fix is as easy as changing a variable in a lua file.

I know you like posting that image, and I am looking into it now, but don't expect the same results from an aircraft in flight to one strapped down and locked in place.

 

 

 

Because it's easy to change something doesn't make it right, as stated, I am looking into it.

Then you have to change the guns of the russian aircraft.

And then you would have to make new kinds of ammo for the M61 used by static defenses like

Close-in weapon system of every US ship

M167

M163 VADS

which should have the 8 milliradians diameter dispersion.

Otherwise it isn't consistent.

I know you like posting that image, and I am looking into it now, but don't expect the same results from an aircraft in flight to one strapped down and locked in place.

There is a real Hornet pilot in this thread who commented on the matter:

..... there was never any "dispersion" designed in to the gun. It was simply the MOA accuracy due to manufacture defect tolerances.

 

Find the MOA of the gun and you will have the "dispersion" you are looking for.

And then someone else posted the manufacturer's data:

With these facts, we can say the DCS Hornet is either correct, or it's incorrect and needs to be fixed. I don't see the need for 6 pages of long winded discussions and clutter.

For the Tomcat, it's

Da0 = 0.001,

Which seems to equal 10mils, probably for 100% circle.

GD specs is 8mils, 80% circle. Now how do you get the 100% one?

The area of a 8mils radius is 201.06mils² (I know there's not such unit, but we can calculate with that or just use sqft or something else instead). If that covers 80% of the hits minimum, the maximum area to cover 100% is 251.33mils², that divided by Pi and square rooted is 8.94mils. So even the HB gun could still be a bit better to match the GD specs, but this may just be to accomodate for the thing being used in flight. Also, my calculation would take into account that the bullets spread evenly across the circle, which they probably wouldn't IRL - most of them would be biased directly around the center. And as we all (at least those who've got the F-14B module) know, the Tomcat's one is good enough.

I really wish this gets changed. Having to shoot at point blank when Betty already calls for a pull up in order to be effective in A/G at all is just way off. Also in regards of aerial gunnery, correcting the spread would make hitting things harder - but when you hit, you'd hit it harder at the same time. The water can we have now makes it pretty easy to put a few bullets on another aircraft without even aiming properly...

And having future modules like the F-16CM or the F-4E in mind, these reports would keep coming up again and again even more often, because they have a point.

It would be good to see this fixed. Currently it feels way too much like a garden hose.

(...) the manufacturer's data (...)

The manufacturer's data says nothing about the test conditions. Bolting the gun to a solid test bench is not necessarily comparable to firing it from a plane. Vibrations from recoil doesn't change the dispersion of the gun itself, but it does change where the gun is pointing.

And then someone else posted the manufacturer's data:

Which is:

- an advertisement

- probably lab-tested

- highly dependent on mounting platform

The manufacturer's data says nothing about the test conditions. Bolting the gun to a solid test bench is not necessarily comparable to firing it from a plane. Vibrations from recoil doesn't change the dispersion of the gun itself, but it does change where the gun is pointing.

Which is:

 

- an advertisement

- probably lab-tested

- highly dependent on mounting platform

https://www.military.com/video/guns/machine-guns/m61-vulcan-20mm-cannon-on-f-106a/3732679073001

The M61 Vulcan 20mm cannon, an electrically fired gatling gun, is tested on a US Air Force F-106 fighter-interceptor in October, 1969.

Don't you think the government would sue the manufacturer if the advertised dispersion is wrong?

I don’t think anyone is disputing that a stock M61 Vulcan shoots 8 mil 80 %. However the gun can be rigged to shoot a wider dispersion pattern. This development report from 1962 discusses the type of rigging needed to change the pattern. https://apps.dtic.mil/dtic/tr/fulltext/u2/290637.pdf

They modified the gun to fire 3 dispersion patterns which varied from the base pattern. First was a wider pattern with a high azimuth to elevation ratio ( and oval), The second was a larger circular dispersion pattern of 14 to 18 mils. The last pattern was a tighter dispersion pattern with a diameter of 4 to 6 mils. This tighter pattern could not be achieved during the tests.

The oval pattern was achieved by modifying the barrel clamps. Which essentially changed the barrel length, in order to produce barrel whip. This resulted in an oval pattern of 50 mils in azimuth and 12 mils in elevation. Or 38 mils in azimuth and 8 mils in elevation, depending on the barrel clamp. The air defense version of the Vulcan operated by the Army, the M167, was issued with a similar barrel clamp for anti personal use. This barrel clamp is pictured in the manual for the m167 along side the stock circular barrel clamp.

The 14 to 18 mil increased pattern was achieved by shimming the barrels at the barrel clamp. This increased the effective barrel length which resulted in a larger circular pattern of 16 mils 83%.

This is what Yo-Yo was talking about in his previous post, the gun can be rigged to fire a variety of patterns and was done so operationally.

He indicates that the gun on the Hornet is specifically rigged to shoot a wider dispersion than stock. If you wanted to find if that were true you would probably need to read the A1-F18AC-750-300 and A1-F18AC-750-100 manuals and see how the barrel clamps are rigged.

Your estimations are quite rough based on "3 mils for 2A42" . 3 mils is close to this value, but it gives an opportunity to understand what is used as a measure of dispersion.

As the ratio is close to 8, any military can say that it is MEDIAN - app 8 times less then full dispersion (or diameter).

So, 0.0022 will give about 17.5 mils. Why it was choosen? There was an information that the cannon has different barrel clamps to obtain different dispersion patterns.

He then goes on to state that the setting Da0 in the shell table is not the dispersion ratings in milliradians (mils). Putting .008 into the shell table won’t give a you a dispersion of 8 mils aka .008 radians.

He states, a Da0 .0022 = 17.5 mils for the m61 and that 3 mils = .004 Da0 for the BMP gun. It’s implied in his statement, that the total dispersion is greater than median dispersion by a factor of 8, and the ratings given by militaries, in mils are the median dispersion.

If I’m reading his comment correctly, the formula for dispersion in mils is:

dispersion in mils = Da0 (from shell table.lua) * 8

This seems to hold true to the examples provided earlier (.0022 Da0) = 17.5 mils and .0004 = 3 mils

17.5 mils ~ .0176 radians = .0022 *8

And

3.2 mils = .0032 radians = .0004 * 8

It also explains why the Tomcats Da0 is .001 as it results in an 8 mil circle, which is apparently spec for the gun.

8 mils = .008 radians = .001 * 8

If you wanted to figure out another gun the formula would be

mils/1000 / 8 = Da0

So if you wanted to mod the GAU-8 with an accuracy of 5 mils

The setting in the shell table should be

5/1000/8

Da0= 0.000625

Cool. Thank you very much NineLine. Please remember we have eye witness testimony of A2G strafing from a Hornet pilot. It may just be that there is a calibration problem or execution problem between the files and the code or the files and the engine, that sort of thing. Even though the math is not working out perfectly, tweaking it for game play, in-game realism and FUN will sell copies.

I have talked to Yo-Yo about it, and there does seem to be some room for improvement, I will let you know when I know more. Thanks.

 

PS this is just the Hornet gun right now, once I know what's going on I will ask about others, but please don't skew this discussion on to your favourite gun in the game.

The shell_table.lua has these values. This means the dispersion is dependent on the ammunition, and not the gun itself or the rig. What this leads to is every plane using the M61 will have these spread patterns.

I looked around the forum and the issue seems to be for the F15, too.

I have read a report on how these clamps have not been used in combat, so shouldn't the Hornet get the stock clamp, that is widely used?

If written data or ground tests aren't enough, the only way to figure it out (short of getting in your plane and shooting at the ground) is to find a video of an F18 shooting, and the impacts, where you can work out the firing range and target width. Like, Axalpa, or something.

There's got to be a clip somewhere that has the required data.

Edit:. Or even just a video of the F18 HUD while firing. You just have to see the tracers filling the gunsight ring, which is a known angle.

Well the F-106 test is a good example of that already. A couple points to keep in mind:

1) To me, "dispersion" IS the median, or already includes it as a matter of fact. Let the sim engine find the median, according to dispersion. [if needed an 85-90% circle would be just great compared to how it works now. Lots of room between 80 and 95%]

2) Mounted to the airframe or "in flight" ... don't get lost in Einstein's Special Theory of Relativity here. The gun system should function independent of the flight dynamics and fire relative to the airframe. Unless you are seriously modelling g loading and such for jamming, nothing more is needed. We already have barrel warp and that has problems too. The airframe will pitch and roll and "rope a dope" plenty all on it's own. That is already modeled and rendered via the aircraft. Errors and inaccuracies seem over modeled at times and double stamped for some reason. And of course, some weapons are just fine on other aircraft and units. Please don't bring up the "third party argument." If you allow it in game, including the inconsistencies, you endorsed it.

To recap, don't get hung up on "medians", we are already dealing with "dispersion."

Don't get hung up on "in flight", the sim already models that.

It could be we are dealing with unintended "double calculated rendering" in the math for some aircraft, weapons, and shells.

To get a general idea:

@8:10

The firing range targets

Both the F-5E and F/A-18C employ a 20mm cannon to fire at two types of ground erected targets. Firstly there are pairs 20 foot (6m) wide orange Day-Glo cloth targets on the mountainside facing up and down the valley. A second type of target employed is a pair of 6 feet (2m) square orange metal panels which are bolted to the rock. The nearest pair of targets are erected just 750 feet (230m) away from the crowd line.

Left to right Two west facing 20 foot (6m) wide orange cloth targets (left) were erected for each days flying. The dust and numerous holes were a result of several passes from the F-5E Tiger IIs and F/A-18C Hornets firing from their nose mounted cannon.

Sparks fly up from around the orange metal panels which are bolted to the mountainside, as the ammunition ricochets off the surrounding rock.

Northrop F-5E Tiger II (J-3068 ) firing from its two nose mounted Colt-Browning 20mm M39 cannon. The F-5E was firing between two groups of spectators at targets that were no more than 250 yards (230m) away from the crowd line.

F/A-18C Hornet (J-5014), descending at a 10º angle of attack, to fire in bursts of 240 rounds at the target.

Good example. For comparison, a BMP-2 is 6.7 meters long.

Can't work out a precise value without the range, but given how gently the pilots pull up after the attack, it's further than I normally shoot (G override every time to avoid the ground).

So the pattern width is within a vehicle length, at a non-suicidal distance. This is not the case in DCS.

Edit: In-game test. I started shooting one second after the break X started flashing. Pulling away from the hill caused greyout and I just missed the trees. I think it's fair to say the Axalpa shooting distance is further, yet the in-game pattern is twice the size.

One more thought; even if, in theory, clamps can increase the dispersion, the sim should model them without. Equipment in the sim is usually portrayed in an ideal state, not a degraded state. Like how the Ka-50 gun has practically no dispersion despite it being a flexible mounted helicopter gun, optics always track perfectly, gun computers always have perfect information from the sensors, and muzzle velocities are always to manufacturer spec, with no account for wear.