Russian guns balistics...

[1PL-Husar-1Esk]

True. In VR aiming is much easier.

I wasn't thinking about VR, btw where shooting in VR at discussed ranges is pointless with obvious reasons. My point was shooting in 2d is easy compared to real life. Dispersion and effectiveness of types of gun platform and projectals should be realistic despite possible hits from very long distances because of virtual pilots experience and lack of other not simulated difficulties.

[-=PHX=-SuperEtendard]

Ok, back on topic with a bit of testing and some pictures

 

First a comparison of how a target at around 700m away appears on both the German and Russian gunsight.

 

 

 

 

 

 

You can see that the German gunsight is "smaller" (has less mils) than the Russian one, if i'm correct it's like 140 mils wide for the Russian (inner circle) and 100 mils wide for the German one. So one thing to notice if you use both gunsights with zoom levels so that they have the same ring size in your screen, in the Russian one you will see things smaller than with the German one at the same distance, like in the images above, both planes are at around 700 meters away yet it looks much closer in the German one.

 

Then I tested how much vertical lead is needed to hit the straight flying 109 F-4 in the 72AG training server at around 700 meters, with the 20mms and the 15mm, with 250 meters convergence. The pictures show the position of the gunsight when I fired the round that hit the plane some moments later.

 

 

 

 

 

 

This last one was with the 15mm and was a bit of a side shot, as I wasn't right at 109's six, but in the vertical perspective it should be the same.

 

 

You can see the trajectory of the MG 151/20 makes it drop more than the other two. The 15mm does have nice ballistic properties, close to or even a bit better than the ShVAK. For the ShVAK it's like 5 mils of vertical lead, for the MG 151/20 around 15/16, and for the MG 151/15 maybe 3 or 4 mils.

Edited September 18, 2017 by -=PHX=-SuperEtendard

[-=PHX=-SuperEtendard]

Finally the gun dispersion when firing a continuous burst, also at 250m convergence and at full zoom so all of the pictures are comparable.

 

 

 

 

 

 

 

 

 

 

The MG 151/20 has more dispersion than the ShVAK and the MG 151/15, you can also see the vertical drop, the lesser the drop the more concentrated the bullets are in the vertical axis. Also the horizontal dispersion is a bit random and sometimes gives better or worse patterns with each salvo. The ones above were the ones I considered "normal" or "common". But for example in the MG 151/20 I had two cases in which it was worse and better respectively (not as common as the one above).

 

 

 

 

 

 

 

 

 

So to give a bit of dimension to the horizontal dispersion, I took this worst case for the MG 151/20 and overalapped it with the image taken from a 109 at 720 meters away also at full zoom so they are comparable.

 

 

 

 

 

 

 

 

You can see the dispersion can make you miss a particular part of the plane you aim for (like the tail or the cockpit) but isn't really enough to miss the plane entirely imo (the rounds are within the target's wingspan), so I think if a player gets the vertical lead right it wouldn't have much problems in hitting the target at these ranges (or at least if it misses I wouldn't say it's because of the lateral dispersion alone).

 

 

 

Now I don't know if this is how these guns behaved IRL, if we could get some cuantitative data for comparison, like dispersion area vs distance it would be nice. I think working with the lateral mils of the gunsights and knowning how much they drop vs distance we could calculate more or less a dispersion area like this?

 

Edited September 18, 2017 by -=PHX=-SuperEtendard

[unreasonable]

Interesting. Now everyone knows where to put the pipper and there will be even more long range kills.

 

One pedantic point - what you are showing is not actually just the dispersion, because you are firing a burst and the earlier shells have dropped further than the later ones. Dispersion is the measure of the spread of the impacts at a given range. You could have zero dispersion and you would still see a vertical pattern.

 

I do not know how many shells in total, or tracer/non tracer ratio, but if you know the length of the burst and simply assume the shells drop according to g, you could estimate the part of what you are seeing - in vertical "dispersion" -  is actually due to the time difference between the first and last tracer.

 

edit - and before someone mentions that the fired shots drop a little (a very little) less than a dropped shot, I did say estimate.  

Edited September 18, 2017 by unreasonable

[-=PHX=-SuperEtendard]

Yes I agree, but with the last pictures I was looking into lateral dispersion rather than vertical (I should have pointed it out).

 

With vertical dispersion you also have the different velocities between HE and AP making different drop trajectories so both effects are combined in the burst vertical pattern. Making it hard to conclude "X gun is less accurate than Y" while it could be that X gun's ammo has more velocity difference than Y gun's while both have the same accuracy.

Edited September 18, 2017 by -=PHX=-SuperEtendard

[unreasonable]

OK got it.     So what I take from this is that you are saying is that all these guns fire a pretty tight group, the aiming issue is primarily about getting elevation right....?  

[JtD]

I ran a couple of tests myself. I used my damage mechanics check shooting range for that purpose.

 

I fired at a LaGG-3 from 500m out. I used a LaGG-3 and a Bf109G-4 for that. I had the engine running, at about 30-40 throttle. The shaking due to the engine was not excessive this way, in fact, I found no impact comparing to shooting with engine off. What rounds are we looking at:

Projectile data: projectile weight, muzzle velocity:

ShVAK, AP: 20mm, 96g, 750m/s

ShVAK, HE: 20mm, 96g, 770m/s

MG151, AP: 20mm, 117g, 720m/s

MG151, HE: 20mm, 92g, 790m/s (Mine)

 

I recorded tracks, and evaluated with observation and Tacview stats. From the Tacview stats it is easy to give projectile velocities, average over distance, as time of firing and time of hit are being logged. What I got:

 

In game results for average speed to 500m distance:

ShVAK, AP: 610m/s average

ShVAK, HE: 600m/s average

MG151, AP: 535m/s average

MG151, HE: 525m/s average

Without knowing the specifics of the rounds modelled (various AP and HE existed), I can confirm the MG151 data to be about right, matching historical ballistic data.

The performance of the ShVAK is very odd, I see absolutely no reason for it to maintain velocity that much better. If the wiki information is accurate, the in game performance is simply BS.

I've found a ballistic data table for the ShVAK, assuming a muzzle velocity of 800m/s. It gives a flight time of 0.8s, but the whole table does not make a lot of sense to me. The game is modelled in agreement with that table.

 

Next thing is accuracy, I fired very short bursts, 2-3 round, every 2-5 seconds. Gun overheat was no issue in this test. What can we see:

Ballistic arch is there for both, but larger for the MG151 (mandatory consequence of the slower velocity). Not really visible in the pictures.

Average accuracy is way higher for the ShVAK.

Worst case accuracy is way higher for the ShVAK.

 

Conclusions:

Compared to the MG151 the ShVAK is the sniper weapon the OP claimed it to be.

The behaviour of the MG151 appears about right.

The performance of the ShVAK should be checked, it is not plausible.

Edited September 18, 2017 by JtD

[Max_Damage]

There s no secret in damage modeling. Han has commented on it and mg151 20 does ~20 % more DPS compared to a shvak.

Edited September 18, 2017 by Max_Damage

[JG13_opcode]

There s no secret in damage modeling. Han has commented on it and mg151 20 does ~20 % more DPS compared to a shvak.

Unless the aircraft are modeled with hit points like an MMO, I don't see how "damage per second" is a useful metric.

[unreasonable]

I would have though they must have hit points - or at least components have hit points. Plus presumably an armour rating - and perhaps magic resistance.   Not sure how else you could do it without becoming hopelessly complex.  

 

If you think of a weapon as having damage per hit based on the projectile and hits per second based on rate of fire, DPS makes a certain sense as a measure.  I admit seeing DPS made me think of elven archer builds..... 

[JtD]

Unless the aircraft are modeled with hit points like an MMO, I don't see how "damage per second" is a useful metric.

I think it's damage per shot. I also think Han said something different. I also know that my tests showed them to be on par in a round for round comparison. As a gun, the ShVAK deals more damage owing to a higher percentage of AP rounds in its belting.

[1PL-Husar-1Esk]

Unless the aircraft are modeled with hit points like an MMO, I don't see how "damage per second" is a useful metric.

How then you can explain when shooting at wingtip , after some time whole wing collapse?

[Lusekofte]

Come on. You have to admit the Pe-2 is pretty ridiculously tough.

 

You know this tread has become very pathetic, In all these years LW pilots have screamed in this forum about getting better planes and now they want worser oponents. This is a never ending story, and no one here can put a single evidence for their claim. The PE 2 was very rough ,heavy and  its engine had greater tolerance for damage than german engeneering.his was a fact for just about every single moving mechanical part in the eastern front. German engeneering was excellent, witch sometimes worked against them in cold weather and if a bullet hit them.

For us that actually fly them, we see in first pass if this LW pilot will be successful or not. Yesterday a 190 shot down 2 of 3 PE 2 in under a minute with no problem at all, I was the one surviving since he could not find me. This happened in Coconut server.

HE 111 is regarded a very though and good bomber by its crew, but in Eastern front they where put to do work it was never ment to do. Very heavy losses as a result. It got good resilience against small arms in my opinion , but take cannonshells very badly 

Edited September 18, 2017 by 216th_LuseKofte

[Holtzauge]

This is not directed at you specifically Lusekofte but to the biggest collection of whiners we have in this forum. And I’m not talking about the Luftwhiners. I’m talking about the loudest and most forum disturbing crowd around: the Luftwhiner-whiners. This crowd never fails to pop up and it’s always the same story: Anything brought up for discussion about the LW is brushed off as whining when the biggest whining based on anecdotes, book quotes and feelings we have had lately has been about the P-40. Strangely, the same crowd was conspicuously missing there or even pop up here calling kettle black. I wonder why? Surely there is no bias involved right? You just need to read through this thread and see the replies and likes given and compare that to missing same in the numerous P-40 threads to connect the dots. Sorry for the rant but this sanctimonious Luftwhining BS makes me puke.

[BraveSirRobin]

This is not directed at you specifically Lusekofte but to the biggest collection of whiners we have in this forum. And I’m not talking about the Luftwhiners. I’m talking about the loudest and most forum disturbing crowd around: the Luftwhiner-whiners. This crowd never fails to pop up and it’s always the same story: Anything brought up for discussion about the LW is brushed off as whining when the biggest whining based on anecdotes, book quotes and feelings we have had lately has been about the P-40. Strangely, the same crowd was conspicuously missing there or even pop up here calling kettle black. I wonder why? Surely there is no bias involved right? You just need to read through this thread and see the replies and likes given and compare that to missing same in the numerous P-40 threads to connect the dots. Sorry for the rant but this sanctimonious Luftwhining BS makes me puke.

 

The 2 situations are not even remotely the same.  On one hand we have people who fly the P-40 who are complaining that the crappiest fighter in the game is not good enough.  These are people who actually fly the plane.  They have real experience to back up their "feelings".  On the other hand we have 109/190 drivers complaining that the Yak is capable of magical things that should really not be possible.  They want the best fighters in the game to have an even bigger advantage.  However, most of them would not actually fly the Yak on a MP server if you pointed a gun at their head.  

 

Do you see the difference?  

[Holtzauge]

Well that may be your feeling my feeling is different. Got data?

[BraveSirRobin]

Well that may be your feeling my feeling is different. Got data?

 

Every time I see someone complaining about the Yak I check their WOL stats and most have virtually no time in the Yak.  You got data saying that the people with no experience in the P-40 are complaining about it being too crappy?

[BraveSirRobin]

At least the people with no MP time in the p-40 have a good excuse.  It's a pig.  The people who refuse to fly the Yak don't really have a good excuse.  The Yak isn't too bad.

[Holtzauge]

No, I'm saying there is a double standard here. I don't think you should get hung up on the P-40 though. The problem runs deeper than that. Anyway, I'm not planning to continue derailing this thread. I had my say and if you don't agree then we can agree to disagree.

[unreasonable]

I think the problem - deep or not - always arises as soon as anyone brings peoples' motivation for saying something into the equation.  This turns the discussion into rhetoric.  

 

If we want to stay as scientific as we can,  we have to accept that a point is empirically backed and logically made, or it is not. Motive is irrelevant. 

[Holtzauge]

Well from a scientific standpoint then: I have an MSc in aeronautical engineering specializing in aerodynamics and structural engineering and I have done structural engineering on a number of aircraft and based on that I say its fertilizer that AP does as much structural damage and Mine shells so little as we see today in-game in deflection shots. However, it would surprise me if we ever saw a properly modeled Mingeschoss because if we did, there would be no end to the forum whining since my “feeling” based on my professional experience tells me that a Mingeschoss round would blow off whole plywood wing panels or make matchsticks of half the stabilizer/elevator assembly with one round and I don’t envy the developers trying to sell such a change to a community that has gotten used to Mingeschoss firecrackers producing black smoke and little else.

[SYN_Haashashin]

To all,

 

Stop with the personal back and forth of your feelings or any other matter...usually doesnt end up well for all involves parties.

 

Also I do not remember how name times I call people not to label other forum members, still people seems not to read me or plain ignore me...not nice and will have to do something about it if things keeps going the same way.

 

Haash

Edit: About feelings...It has been said multiple times by the team: Feeling or subjective opinios wont be taken into account. Only hard back up real data vs ingame data.

[JG13_opcode]

How then you can explain when shooting at wingtip , after some time whole wing collapse?

Like I said, bad damage models.

[VesseL]

If we could, im sure some of us would do proper scientific tests, but we dont have the tools to do so, i guess. Every test made so far has been shot down.

 

The deep problem is, i think, the same old we vs them. theres the motive, for some. Or even I and I.

[BraveSirRobin]

I think 90% of the "us vs them" issues would be resolved if the people who fly exclusively German started flying VVS more often. At the very least it might allow some of us who are stuck flying VVS to fly German occasionally. But as long as I keep going into servers stacked with Germans, I doubt there is going to be much sympathy for the guys complaining about the Super Yak.

[SYN_Haashashin]

I think 90% of the "us vs them" issues would be resolved if the people...

To me it will end if people finally understand that they may have different opinions and agree to disagree and move on.

 

Then if they want they can elaborate a report on the issue in hand and send it to the devs. They will look at it and if the agree with the data presented they will do something about it.

 

Haash

[BraveSirRobin]

To me it will end if people finally understand that they may have different opinions and agree to disagree and move on.

 

Haash

Try reading the context of my post and you will see that I'm agreeing with him. I'm also suggesting a possible solution for the "us vs them" dynamic.

[VesseL]

Try reading the context of my post and you will see that I'm agreeing with him. I'm also suggesting a possible solution for the "us vs them" dynamic.

Im with you, and so is Haashashin i think.

[Venturi]

This is just the lead vs feathers example, all dressed up. Baloney.

 

1)  Take two identical cannons firing identical shells at the same initial muzzle velocity.

 

2)  Now make the shells so that one contains a slightly denser inner core - the weight is different but the size, external shape and finish are identical.

 

3)  Fire them again at the same muzzle velocity - which will take a larger charge (edit - or possibly longer barrel) for the heavier shell since a greater force is required to accelerate the greater mass from rest to the same velocity.

 

4) The shells have the same drag - so the air resistance exerts the same force on each shell. It will decelerate the heavier shell less, so it will have a flatter trajectory, ie a greater range.

You are describing Sectional Density - not mass per se. Since an increase in mass with a concomitant increase in frontal area would not make the round any better aerodynamically. As wiki states: "the ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight.^[1] It is inversely proportional to the negative acceleration: a high number indicates a low negative acceleration--the drag on the projectile is small in proportion to its mass."

 

BALLISTIC COEFFICIENT INCORPORATES MASS.

 

This is just simple physics. But if you want to do it in ballistic coefficient terms Yes, the only terms that matter in this argument. As I said and as wiki says on the page you liked.

 

Here we are from Wiki:

 

" The formula for calculating the ballistic coefficient for small and large arms projectiles only is as follows:

BC = m/ (d^2 . i)

Where:

BCProjectile = ballistic coefficient as used in point mass trajectory from the Siacci method (less than 20 degrees).

m = mass of bullet

d = measured cross section (diameter) of projectile

i = Coefficient of form"

 

Note that the formula for ballistic coefficent contains mass as the numerator!  In other words, as in my thought experience, if the terms d and i are the same for two shells, the difference in BC is down to mass.

 

IF THE TERM i is the same! It is NOT! It is how the mass is shaped that matters most and your lack of explanation of the importance of the denominator in this equation says it all. I like your little end-run around an honest explanation here so I'll go a little further to make my point, then I'll be done. It's easy as my point is made just a little bit lower on the wiki page you like:

 

BC = M*i^-1/A

 

where i is the object's general ability to move through a fluid medium.

 

Sectional density is ALSO important - it is the ratio of an object's mass to its cross-sectional area with respect to a given axis, divided by A. It conveys how well an object's mass is distributed (by its shape) to overcome resistance along that axis.

 

I really do not know why this is causing so much confusion. Because you are making it so. A clear explanation of this would be: The AERODYANMIC PROPERTIES OF THE PROJECTILE are the MOST IMPORTANT CHARACTERISTIC to its ballistic trajectory. That is what I said earlier, and it is correct. I even provided an explanation: why a round tipped, heavier bullet will drop more than a sharp-tipped, lighter bullet if both are fired at the same muzzle velocity.

 

Mass has NOTHING to do with it, other than to characterize the BALLISTIC COEFFICIENT, which for two shells of equal caliber, will come down to the term i! (and yes mass of course.) The fact that the denominator is MULTIPLIED by i means everything! A smaller i will give you a smaller area, essentially making your projectile much denser in regards to aerodynamic properties.

 

 I have said that I would be surprised if the ShVAK's trajectory was flatter than that of the  Hispano's since the latter has a heavier shell with the faster muzzle velocity, not that it was impossible. You say if a projectile is heavier, then it should have a flatter trajectory. Then you say it's not impossible to be the reverse. You make no sense, except insofar as you are saying the same thing I am!

 

If someone has specific facts about the two shells - or cannons - in question that would explain how the ShVAK's trajectory can be flatter, please post them.  You need the Ballistic Coefficient. Or at least a general shape of the shell which might give a rough idea of the term i. I would say that they are probably pretty equal in shape - and so equal in the term i - and thus all other things being equal, a more massive projectile with equal diameter will be longer and WILL HAVE A BETTER BALLISTIC COEFFICIENT. Therefore, the Hispano should have better trajectory at extended ranges.

 

Now why was that so hard?

 

Essentially, a heavier bullet with exactly the same frontal area and aerodynamic form will have a higher ballistic coefficient! And that's ALL that matters!

 

 

 

edited to fix typos caused by multitasking. now back to my job.

Edited September 18, 2017 by Venturi

[ITAF_Cymao]

I hardly imagined you were damaged at all or ok maybe in hainkel 111

Don't need to shoot from a distance to a H111, a russian pilot can park his plane on a H111 without damage...

But sometimes it happened when I was flying by the fighter.

 

S!

Edited September 18, 2017 by ITAF_Cymao

[Guest deleted@83466]

Don't need to shoot from a distance to a H111, a russian pilot can park his plane on a H111 without damage...

But sometimes it happened when I was flying by the fighter.

 

S!

 

 

True, but only when they start their attack from whine o'clock high.

 

[mb339pan]

old, old story...

 

https://forum.il2sturmovik.com/topic/16784-yak-can-keep/?p=270480

 

 

 

[unreasonable]

Venturi, I will just address one point from your extraordinary rant, since it sums up your whole problem of lack of reading comprehension.
 
"I have said that I would be surprised if the ShVAK's trajectory was flatter than that of the  Hispano's since the latter has a heavier shell with the faster muzzle velocity, not that it was impossible. You say if a projectile is heavier, then it should have a flatter trajectory. Then you say it's not impossible to be the reverse. You make no sense, except insofar as you are saying the same thing I am!"

 

I said, perfectly clearly, that a heavier shell would have a flatter trajectory, other things being equal. I am sorry that this seems to be a difficult distinction for you to grasp - no-one else in the thread appears to have any difficulty with it. 

 

In the case under discussion, we know the MV. Hispano is higher.  We do not know the coefficient of form. The ShVAK shell would have to be much more aerodynamically efficient than that of the Hispano in order to compensate for the weight and MV factors. In fact, the term i, the coefficient of form, would have to be about 1.4 times larger for the Hispano to give it's shell the same ballistic coefficient as the ShVAK, based on the wiki numbers.  Given that these are two similar looking cannon shells designed for much the same purpose that would be unlikely. Not impossible.

 

If indeed it is not true, please show us the data.

 

Now stop making a fool of yourself.  

 

 

 

 

 
 

[150GCT_Veltro]

Please don't pretend like it's an isolated occurrence.

 

It is not.

 

This He-111 took 6 rounds of ammunition and was destroyed:

 

DAMAGE_1.jpg

 

This Pe-2 took 162 rounds of ammunition and was destroyed:

 

DAMAGE_2.jpg

 

 

This is reproducible. It is not some random, cherry-picked aberration. It happens constantly online.

 

This is another frustrating and discouraging aspect of this sim. Is almost useless escorting bombers because of these VVS ammo.

 

Somebody still says "Luftwhiners", may be just to troll a bit or only to make closing this thread, i don't know but really, i don't get the point of people who still says that VVS ammo / weapons are not overmodelled.

Edited September 19, 2017 by 150GCT_Veltro

[Kurfurst]

 

Now I don't know if this is how these guns behaved IRL, if we could get some cuantitative data for comparison, like dispersion area vs distance it would be nice. I think working with the lateral mils of the gunsights and knowning how much they drop vs distance we could calculate more or less a dispersion area like this?

 

 

 

Nothing easier than that - 100% hit probability (if you wish to compare it for 50%, 75% etc. hit probability, you need to convert it first, usually with Gaussian distribution) dispersions for MG FF, MG 151/20 etc. 

 

Take note that the report notes that "The dispersion of the MG 151/20 weapons is.... extremely small" , i.e. at 1,9 mils for 100% dispersion (dunno what to say about the MG FF's shocking 1.0 for 100%, but hey, its Swiss after all).

 

Edited September 19, 2017 by VO101Kurfurst

[Fern]

Question of the day

 

When was the last time you were "sniped" a German?

[JtD]

"The dispersion of the MG 151/20 weapons is.... extremely small" ,

It says 'sufficiently small', to be exact. Thanks for posting this data. What's also interesting to note is that 'dispersion increases with barrel length, because weapons with larger muzzle velocities, due to their longer barrels, develop a tendency for barrel vibration'.

 

That's exactly the opposite of what we occasionally could hear on the forums, i.e. the Soviet guns would be more precise because of their longer barrels. It would be interesting to know how they dealt with that and how that is considered in dispersion figures. One would at least have to look at the exact mounting of the gun for any dispersion figure.

Edited September 19, 2017 by JtD

[Finkeren]

Question of the day

 

When was the last time you were "sniped" a German?

 

If we set +500m as the threshold for "sniping" I would say  the day before yesterday. Trying to run away from a 109 in an La-5F at low altitude (had expended my ammo) I was gunned down from around 600m with relative ease (meaning, he didn't fire more than a couple of bursts before I had an oil leak). It was on a "normal" server, so I'm fairly certain about the distance. I've been hit by a German pursuer from much further away than that, especially when flying the MiG, but this is the most recent example.

 

Nothing wrong with that really. I presented an easy target to hit, flying straight and level, so naturally he took the shot.

 

As I've said now repeatedly: The reason you don't see German pilots taking these hail-Mary shots more often is because they don't have to.

Edited September 19, 2017 by Finkeren

[Kurfurst]

You are right, somehow I read it aussordentlich, I do not know why :D

 

I guess the 'long barrel helps' comed from small arms experience that are mostly single shot weapons, and in that case its beneficial since the long barrel usually increases MV and maked the rifle nose heavy - usually good to eliminate euróra of the shooter. Barrel flexing is seldom felt because the first round already left the barrel...

 

Automatic weapons are quite different however since the accuracy of follow up shots is decreased due to the movement of the barrel. Its easy to see that the longer (and thinner) the barrel and more powerul the munition is, the greater the barrel flexing and dispersion will be.

 

I am quite curious about the dispersion of russian guns, however as the Svak was fairly compact with a weaker round so I except it to be decent. The Hispano on the other hand with its very long barrel and patent round, especially in its wing installation probably has higher dispersion.

You are right, somehow I read it aussordentlich, I do not know why :D

 

I guess the 'long barrel helps' comed from small arms experience that are mostly single shot weapons, and in that case its beneficial since the long barrel usually increases MV and maked the rifle nose heavy - usually good to eliminate euróra of the shooter. Barrel flexing is seldom felt because the first round already left the barrel...

 

Automatic weapons are quite different however since the accuracy of follow up shots is decreased due to the movement of the barrel. Its easy to see that the longer (and thinner) the barrel and more powerul the munition is, the greater the barrel flexing and dispersion will be.

 

I am quite curious about the dispersion of russian guns, however as the Svak was fairly compact with a weaker round so I except it to be decent. The Hispano on the other hand with its very long barrel and patent round, especially in its wing installation probably has higher dispersion.

[unreasonable]

I wonder how the developers have approached this. If they have modeled each gun according to separate test documents, each of which did not test all the weapons, they may have built in results to each gun that were actually affected by different test conditions. 

 

An alternative approach would be to use all available information to produce a generic 20mm cannon ballistics table, then alter it for each gun based on variables  that are known to affect results in a systematic way - eg barrel length as discussed in Kurfurst's document (which I cannot read ),

plus what is known about the other variables such as shell weight, MV and variations due to shell shape etc, not to get the figures back to the original test data, but only so far as the individual inputs are known to affect the results in a systematic way.

 

This has the benefit of averaging test conditions variances out over the different guns.  The disadvantage is that you will end up with none of the results quite matching the test results.