Damage mechanics (contains NO SUGGESTIONS)

[JtD]

With firing rounds at aircraft expecting them to go down being the main purpose of this game, and recurring discussion about various aspects, I've noticed in the past that maybe an overview about how things work in general could be useful. This way we could replace some of the 'emotion' with a more analytical approach. I'll start this off with a couple of posts, but as this is technically, physically and historically very complex, I'd be happy about any contributions.

 

Damage principle - damage types / projectiles

 

Punching holes:

 

The most basic principle of a round doing damage is a round punching holes. The round goes in, and if not stopped by something massive, goes out on the other side, destroying everything in its path. In WW2, simple steel rounds were available for many guns, typically referred to as AP (armour piercing) rounds. The purpose of these rounds was to hit something critical, even if protected by armour, and put a hole into it. While there are many systems on a WW2 aircraft that can be considered critical, AP rounds are most effective if they hit the engine or the pilot. They are ineffective against general aircraft structure, because if there's nothing critical to hit, they just leave a hole on the entry side, and another on the exit side. Even if they hit load bearing members like a wing spar, the effect is often uncritical. Testing found that hits to load bearing members would typically only reduce the durability of the air frame, but not prevent it from returning to base - provided extreme manoeuvres were avoided.

AP rounds are fairly ineffective when hitting fuel tanks, as they are only capable of producing small holes, which can be sealed by the tanks self sealing features, and only create a minor risk of fire.

AP rounds hitting thicker material like armour plates will also create splinters, even if breaking up, which can cause damage different to just punching holes.

 

Fires:

 

One of the biggest dangers on board of an aircraft is fire, so naturally, trying your best to light up the enemy, is a good approach to damaging it. Most of the common guns in WW2 came with some sort of an I (incendiary) shell. Materials typically used for the incendiary effect would be phosphor, magnesium or aluminium - often in a mixed composition like thermite. Obvious targets for these rounds are fuel tanks, but large inciendary rounds are capable of setting anything on fire, including aircraft structure. Pure Incendiary rounds are typically poor at penetration, some of the smaller rounds could be stopped by the aircraft skin at shallower angles of impact. Penetrating into fuel tanks proved problematic for smaller calibres, too, rendering the rounds ineffective.

Incendiary elements were often added to rounds with other basic concepts, like API, armour piercing inciendary or HEI, high explosive inciendary. API rounds were very capable of holing fuel tanks and igniting the fuel, something neither pure AP nor pure I rounds were capable of. HEI rounds were often more damaging then pure HE rounds. Interestingly, HEI fillers often have higher relative effectiveness factors than the HE they replaced, meaning that 1g of HEI is overall more damaging than 1g of the HE. The inciendary material was typically burning slightly longer and hotter than the explosive, increasing both blast pressure and the chance for fire.

 

Splinter:

 

Splinters rely on the shotgun approach - instead of one massive round, dozens or hundreds of smaller fragments tear through the target, hoping to hit something critical. This shotgun effect is achieved by having the round blow up upon impact or slightly delayed inside the target. Shells of that type were used by all nations for weapons of heavy machine gun size and up, and are typically desgnated high explosive (HE). HE rounds, together with AP, are the two 'standard' type rounds for cannon sized guns. Depending on the explosive and the shell used, there were various subtypes. The explosion of the round makes splinter go in a cone shaped pattern from the point of entry, giving them a much larger area of destruction than an AP round. Compared to the solid AP holes, splinters lack (armour) penetration capacity. They are good for damaging systems - hoses, pipes, containers (including fuel tanks), radiators - and do more structural damage than an AP round. Against aircraft skin and light internal structue, the damage might easily be ten times as much. However, the effectiveness here is still to be considered low, still not destroying sufficient general aircraft structure to make a difference. It's also not more critical against heavy load bearing members than standard AP.

 

Gas shock:

 

While standard HE shells rely on the splinters to do the damage, a side effect of having a round explode after impact is that a lot of hot gas is being produced. This gas, even more so than the splinters, is going very fast and, just like the splinters, contains a lot of kinetic energy. If you like, this gas pretty much does the same splinters do, but at a molecular level. It offers no penetration capacity, but spreads out the damage over a really large area. Where an AP round will punch a hole into a panel and the splinters will punch a hundred small holes into the same panel, the gas shock will just take the entire panel off. Due to the high speed, it also works into all direction, not just in a cone shaped pattern starting at the entry point. This makes gas shock very effective against general aircraft structure, provided that surfaces and panels are of any structural relevance. Gas shock has an extremely short range, which largely depends on the amount of explosive used. It is completely ineffective if a too small amount of explosives goes off inside a large empty space. While gas shock is a side effect of HE rounds, the only nation to make explicit use of it was Germany, with the mine shells. These shells contained roughly twice the explosive standard rounds of the same calibre did, at the cost of a weaker shell. The mine shell had an extremely low penetration ability, and did not create as many splinters as typical HE shells did.

 

Gas pressure:

 

Gas pressure is similar to gas shock, but it's not the same. Until the gases created in the explosion eventually go somewhere, the compartment containing the gases will be subjected to extremely high internal pressures. Gas pressure works in all directions and will eventually go the way of the least resistance (whereas gas shock will go on straight until it is stopped). The pressure will cause ruptures, through which the gases can escape, thereby lowering the the pressure, until it is equal to the surrounding pressure. While this can be good against structure, the effect is most evident when the pressure is created inside a closed container like a solid fuel tank, in particular with lots of fuel in it. The gas pressure will cause a fairly large scale rupture, through which a lot fuel is being pushed out in the process. Self sealing tanks will probably have little difficulty in sealing the tank quickly, because the rupture by it's nature is not very wide.

Gas pressure also work well in conjunction with splinters, because structure weakened by splinters will be more vulnerable to ruptures caused by gas pressure. This is particularly true for fabric covered surfaces, which provide very limited resistance to rupture.

 

Damage principles - structure types in view of structural damage

 

Fabric covered (steel) framework:

 

Some aircraft, most famously the Vickers Wellington, are simple steel frames covered with fabric. In game, this type of construction can for instance be found in the rear fuselage of the Yak or on the I-16 (wooden/steel frame). The steel frame carries the loads, the fabric guides the air - providing lift, stability, control. Basically, it is fairly difficult to destroy the structural integrity of such a construction, as the individual steel rods are unlikely to be hit and if so, unlikely to be damaged suffciently to instantly fail and if so, there typically is a redundant rod which can take the load and still keep the aircraft airborne. So if you think about structurally destroying the aircraft, the steel framework is pretty tough. It is much easier to go for the fabric. The fabric, being exposed to high speed air in flight, is under a lot of stress already. Damaging it even slightly can cause significant damage by letting the air do the work. It was found that AP rounds are more or less completely ineffective here, splinter damage, tearing a multitude of holes being of much higher lethality. Gas pressure, creating large scale ruptures, worked reasonably well enough, too. Keep in mind that a ruptured or holed fabric allows high pressure air from below the wing to stream into the low pressure air above the wing, rendering a wing section ineffective even if large parts of the fabric are still there.

Gas shock isn't much of a topic here, possibly due to the fact that the fabric typically spanned over large areas, and didn't come in small panel sized pieces. I suppose the effects of gas pressure are of bigger importance. Incendiary ammunitions could set the fabric on fire with comparative ease, but even here, the fire wouldn't typically be going on by itself.

 

Plywood/Aluminium covered (steel) framework:

 

Another fairly common construction method, particularly among the earlier aircraft, were steel frames covered with panels, be it (ply)wooden or metal ones. The Ju 52 is a classic example, but the parts of the Yak fuselage that isn't a fabric covered steel frame, is a panel covered steel frame. The structural behaviour of such a construction is fairly similar to the fabric covered framework, the major difference being the higher resistance of the skin (panels vs. fabric) to the high speed air. Getting torn to shreds by it was a much lesser issue for the panels, wood or aluminium. On the downside, wood cracks fairly easily, so gas pressure and splinters work fairly well here. Also, gas shock factors in, as panels can be blown off, this is true for both plywood and aluminium. Incendiary would be of even less use than against fabric.

 

Wooden construction:

 

Occasionally, parts of the aircraft structure were made of wood. Such as on the Russian fighters we have in game. Typically, this still followed the frame approach, separating load bearing structure from aerodynamic surface. Compared to a steel frame, a wooden frame is less damage resistant. For the same strength, the wood can be lighter, but requires more room. The extra room implies it is easier to hit, and wood can't take damage as well as steel can. A hit that might be deflected by a steel tube, would probably not be deflected by a wooden bar. Additionally, the extra volume required by the wood will leave explosion gases less room to expand and escape, leading to larger effects of both gas shock and gas pressure. Wooden framework isn't more vulnerable to fire than a steel framework is. Both have no inclination to burn on their own in the air, and where wood might eventually be burnt through by an oil fire, steel might just melt.

 

Aluminium monocoque / stressed skin:

 

In a completely different approach to the above stands the aluminium monocoque construction. It uses the aircraft skin as a load bearing member, thereby reducing the aircraft weight. Spars, ribs and other load bearing members found on classic framework construction could all be reduced without any cost in strength. The DC-3 is probably the most famous early aircraft that incorporated this construction method. In game, most of the aircraft have this type of construction. Compared to the framework designs of earlier time, the monocoque construction was found to be even more resistant to AP and splinter damage. This is owing to the fact that with most of the load being carried by the aircraft skin, the remaining structural members were smaller, less likely to hit and less critical in case of failure. Destroying the load bearing skin was of course more difficult than it had been with the fabric or wooden covered aircraft.

However, as at least the Germans found, this type of construction increased the vulnerability to gas shock and gas pressure damage. Where the frames might lose a structurally unimportant panel, the monocoques lost skin area that was supposed to carry loads. Additionally, as panels on frames where typically fixed with a couple of screws, load bearing skin had to be much better attached with a high number of rivets. That meant that gas pressure, going the way of the least resistance, didn't find an easy exit and would also do more damage, internally, and to the skin.

 

In game tests

 

Establishing a base line:

 

I set up an shooting range that allowed me to fire at the vertical stab of various aircraft at close range. The idea was to just shoot it off and see what happens. I've done this test before with a large number of target and weapon types, but since the power of the mine shell has been adjusted, I've only managed to repeat a couple of tests. The first one was to re-establish the base line. I was firing 20mm round from both a LaGG-3 and a Bf109G-2 at the vertical stab of a target LaGG-3 from 90° off sideways. The outcome of this baseline test was, that it took the ShVAK about 5.1 hits average, and the Bf109G-2 5.4 hits average to completely shoot off the stab. The LaGG-3 vertical stab is of a wooden construction, containing two small spars, plus frames, covered with plywood. The ammunition was mixed, so contained HE and AP rounds of various kinds. It was noticable that occasionally, the rudder, fuselage or vertical tailplane got damaged by splinter damage. Obviously, the rounds don't actually leave holes, and there's no chance for a follow up hit to go through a hole made by a previous hit. The whole system is just about accumulated damage to a section. Against single targets, ShVAK and MG151/20 are about equally hard hitting.

 

Comparing AP and HE:

 

Firing at the same LaGG-3 vertical stab from 90° sideways with the La-5 using pure AP or HE belting, I found no noticable difference. It was a bit hard to keep track. I set it up so that only the right cannon would hit, but I wouldn't swear it worked that way if my life depended on it. Anyway, with nothing structurally relevant in the way, the AP rounds and the HE rounds needed the same number of hits within the uncertainty of measurement. The stab fell off after 5 hits in both cases.

I don't really know why the stab falls off after having received 5 20mm holes, but then I also don't know how it stays attached after having received 5 20mm HE hits. I've said it elsewhere, but repeated for truth: This is completely wrong.

Just as a note from previous testing - lining up 10 LaGG-3's behind each other, one can see that each AP round damages 4 stabs. Each HE round damages 1 stabs. For hits where the path of the projectile crosses more than one component, AP damage multiplies, HE does not.

 

Impact of angle of attack:

 

As the structural damage done by an AP round is roughly equavalent to the length of the path it takes through the target, I was curious if the AP round would improve its performance against the stab when fired at a different angle. So I lined the target LaGG-3 up at 15°, giving the round roughly four times the distance through the stab, including the front spar in the process. It made no difference, within the uncertainty of measurement it gave me exactly the same result as the 90° test. 5 hits it was, again.

 

Ballistics:

 

I checked what effects hitting the vertical stab of the LaGG had on AP projectiles. I was curious about lost energy (lowered projectile speed) and tumbling (decreased accuracy). So I set up a wall some 200m behind the target. I noticed that penetrating the vertical stab appears to indeed cost the round speed, the time between firing and impact in the wall was consistenly longer after having hit the stab than it was without having hit the stab. It was small though, but 1/32 time compression helps detecting even small differences. For lack of certainty I don't want to give a solid number, I'd need to do more testing on this.

I also noticed that tumbling isn't there. Theoretically, a projectile going through the tail of the LaGG would lose stability, and you'd see a higher dispersion after 200m. I didn't notice it. However, I did notice that occasionally with low angle impact, the projectle gets completely deflected away, which in case of a thin wooden skin seems kind of odd to me. These high angle deflection typically appear with a bullet breaking up and individual parts flying off to different places, or hard material deflecting the bullet. Overall, the lack of tumbling/lack of reduced accuracy after penetration is simplified physics, which renders some armour protection concepts less useful than they actually were, the ricochets as they are appear to be a graphics over physics decision.

 

 

Fuel tanks:

 

I figured I'd like to see what hitting a fuel tank does in game. So I set up the poor LaGG-3 again, and fired into the inner wing tank (placed between the two spars and between the landing gear and the fuselage). I was curious about fuel leaks, fires, differences between HE and AP and whatnot. So I fired the MG151/20 of the Bf109G-2, and in the first 10 tries, I found no fuel leak, no fuel tank fire, but every time, after 5 hits on average, the outer wing fell off. I never hit it, but it still fell off. Somewhat puzzled, I switched to the LaGG-3 and tried the ShVAK - to the same result. Well, I thought, lets try with AP only and chose the YVa-23. Still, hitting the fuel tank inside of the landing gear made the wing outside of the landing gear fall off. No fire, no fuel leak, nothing. But the AP could do the trick while firing through the tail, the HE could not. All in all, that was too much to take, I quit testing here. I'm sure I'll try another target, given that the LaGG is one of the oldest planes in game. But not now.

Edited July 31, 2017 by JtD

[Dr_Molem]

A pleasure to read.

 

Thanks JtD.

[216th_Lucas_From_Hell]

Well-executed, thanks for posting this. Looking forward to new tests!

[Retrofly]

I noticed fires seem very infrequent but from lots of gun cam footage fuel seems to ignite easily.

 

I think nearly everytime Ive been shot I've had a fuel leak but it has not ignited. Only once has did my plane actually caught fire and I'm pretty sure that was the engine.

 

Maybe gun cam footage is bias becuase fires are more spectacular so more likely to survive and be propigated but still, I would expect fuel tanks and leaks to be ignited on occasion.

Edited July 29, 2017 by [CBB]RetroflyAxis

[Finkeren]

As usual an incredibly well written and thought-through piece JtD.

 

I didn't find much to disagree with. You definitely point out some things worth looking at.

[keeno]

Really nice interesting read, thanks.

[19//Moach]

I noticed fires seem very infrequent but from lots of gun cam footage fuel seems to ignite easily.

 

I think nearly everytime Ive been shot I've had a fuel leak but it has not ignited. Only once has did my plane actually caught fire and I'm pretty sure that was the engine.

 

Maybe gun cam footage is bias becuase fires are more spectacular so more likely to survive and be propigated but still, I would expect fuel tanks and leaks to be ignited on occasion.

 

 

lots of gun camera footage also comes from the pacific theatre - where japanese planes were notoriously prone to lighting up when hit (no armor or self-sealing tanks)

 

but as you said, most likely this is because footage of things catching fire is largely more spectacular, and this makes them prime choice for documentary filmmakers

 

 

 

now - as for the OP, I found the explanation of AP impact a bit dismissive of how energy transfers from bullet onto metal, causing an outwards-cone style of destruction that widens away from the entry point.  no AP round is perfect such that it would enter and exit without making a larger hole on the opposite side.  this is evidence that energy is being transferred from projectile onto target, and that will cause structural deformation and weakening which has not been mentioned.

 

as you can imagine,  a round impacting metal seen in time-warp photography would look like a blob of putty impacting jello - the kinetic energy involved in such impacts is large enough to cause metal to momentarily liquify. 

 

see: https://en.wikipedia.org/wiki/Terminal_ballistics

 

 

I do not know to how the game depicts the density of AP rounds, and there are many types - however, a "ball round" is a very common general-purpose type of ammunition, and was largely used in WW2.  I would not make the assumption that what the game calls "armor piercing" comprises only rounds of that particular kind.... in fact, it only seems to distinguish round types as "blue" or "orange".... 

 

it is clear enough that "orange" is a round that causes an effect that has about that colour (an explosion)  -- now, "blue" seems more generic, implying only that it does not explode on impact, not necessarily that it is in fact an armor-piercing round specifically....

 

seems to me it regards rounds simply as "HE" or "not HE" - so I wouldn't suppose we should expect these rounds to behave specifically like AP, since they may as well be a compromise between AP and Ball

Edited July 29, 2017 by 19//Moach

[-=PHX=-SuperEtendard]

Nice post JtD. You can also think about the test I did recently comparing the Hispano, MG 151 and VYa-23 HE performance against 109's monocoque wing, in which all three cannons peformed the same. I would thing the MG 151 would perform better in than the Hispano because of the high blast pressure ripping bigger areas of skin. Don't know about the 23mm though as that also has a nice filler although less than the MG 151, but also has a good amount of splinters because of the bigger sheel, so it kinda has best of both worlds?

Another effect I noticed is that it seems that the bounce effect you see sometimes when hitting the ground, water, tanks or even planes looks like it's only aesthetic. In my tests sometimes I had rounds bouncing off the wing, but the explosion and damage done to it were just as normal.

 

 

it is clear enough that "orange" is a round that causes an effect that has about that colour (an explosion)  -- now, "blue" seems more generic, implying only that it does not explode on impact, not necessarily that it is in fact an armor-piercing round specifically....

 

What would be the difference between Ball and just AP? Isn't the ball round the solid steel round? Some of the cannons we have in game, like the VYa-23 and BK 37 feature an inner penetrator, in the case of the 23mm it's hardened steel and for the German 37mm it's tungsten carbide, to be specific these rounds should be labelled APCR rather than just AP, although this nomenclature applies more to tank rounds. Is there a difference between Ball and solid AP (without inner penetrator)?

[19//Moach]

a ball round has a full soft lead core (no tungsten, just lead with a copper jacket) - it is not designed specifically to punch clean through hard things, without the dense inner penetrator, it will squash/fragment and lose a lot more energy into the target than a proper AP will. 

 

thus it may not penetrate all sorts of armor, but it can produce a blast-like effect as it bluntly plows its way through stuff. - it's the basic generic round, aka: "full metal jacket"

 

warbirds historically used a mix of ball/AP/HE and whatnot - it's hard to tell to what extent that is modelled in this game though... in CloD, one could get quite specific about this. I rather miss that here though

Edited July 30, 2017 by 19//Moach

[JtD]

Thanks for the feedback, guys.

 

Moach, I'm not sure I'm getting what you're saying, but if you want to say that 1mm of Aluminium behaves like a block of ballistic gel, I'd disagree. I've also looked at damaged aircraft and it was just that: two holes of similar size, one in, one out. But thanks for pointing to soft/lead core ball ammunitions in general, they may indeed behave a little different than steel slugs, provided they hit something hard or solid. Aircraft skin might not do the trick, a spar or a full fuel tank would.

 

SuperEtendard, in my tests the YVa performs significantly better, both AP and HE rounds than the ShVAK or MG151. It's nearly twice as hard hitting. Your scenario in real life, 3 hits HE from any of these guns into the same spot of the mid wing section would probably be catastrophic. The angle of attack is good for splinters (even AP), because they need to go through most of the wings cross section. In real life, I'd expect the YVa to be a little bit more ahead of the 20mm guns than your tests shows for in game performance. If you were to fire from 90° above, the mine should maintain efficiency, the other HE should lose some, in real life.

I've also noticed that the bounced round damages the spot it hits, however, the projectile does not penetrate into targets behind the deflection spot. So the round is gone, the effect is not just graphical. I don't know if the deflected shot does damage on its new path, yet.

[-=PHX=-SuperEtendard]

In your test with VYa-23 being twice as good in HE vs the other cannons were also at a nearly 180° angle against the mid-wing? It's really interesting. Were you getting consistency in the rounds needed to get the catastrophic failure? In my case it had a lot of dispersion, sometimes 2, sometimes 4 and 5. (in the end the average was around 3 +/- 1)  also it was while flying so don't know if BoS physics would have a significant impact in that (a wing with the same damage would stay attached in the ground, but then in the air it would fall off due to the stress). Also because of the flying targets the hits weren't hitting in the exact same spot, I still aimed and got hits in a relatively concentrated area, around the LW insignia's inner side (basically the outer half of the flap area).

 

About the bounces I saw it with the HE shells, they bounced but it showed the explosion animation and the wing got the damage texture like usual for full hits, the only difference was the tracer flying off from the wing after the hit. A bouncing HE shell wouldn't make much damage other than a dent in the skin I guess.

Edited July 30, 2017 by -=PHX=-SuperEtendard

[ZachariasX]

Maybe one should also have an idea of how shrapnel of an HE 20 mm act on impact/detonation.

 

Telling from the 20 mm Oerlikon HE, when you fire that one against, say 10 sheets of aluminum, each about 4 mm strong and stacked 1 meter in depht, you will see a clean round hole upon impact, this way going throught about the first 3 sheets, then it detonates and create an increasingly big, torn hole (with some small perforations around it), growing to about the sitze of a fist at 3/4 of the these stacked sheets, then the central hole is suddenly small, also leaving a slightly torn hole until it exits through a smaller (1 cm or so) hole.

 

Each of those aluminum sheets was referred to as "1 aircraft" to the hopeless personel in green, operating the 20 mm Oerlikon Flak (the "Mosquito inseminator", as we called it.)

[JtD]

SuperEntendard: No, the testing I did is not the same you did. For one, my setup is static and I can't miss shots. So I hit with a mixed MG151/20 belt. I could add an object to drive through line of fire every now and then and waste shots on that one. But it is a bit too complex for now. I didn't get consistency, but I gave it 50 trials. As I wrote above, the vertical stab goes off on average after 5.1 hits for the ShVAK, but the range is 2 to 10. Anyway, ShVAK's a five, VYa came out with less then three. The same ratio was achieved in shooting off the LaGG outer wing. Flying definitely has an impact, the parts crack completely, and if you apply a load then, like when the aircraft is flying, the things comes off. Static tests on the ground should in general show significantly higher to-hit numbers than tests in the air. I probably should have noted the number until the crack appears, too. Guess I will do that in the future.

 

ZachariasX: Where is that info from? I find it odd that the delay is that large, basically, the round explodes way after it passed the aircraft... German HE rounds at least had an impact fuse (maybe including minimal delay due to physics and chemistry), and it set off the round pretty much as it hit.

Edited July 30, 2017 by JtD

[ZachariasX]

ZachariasX: Where is that info from? I find it odd that the delay is that large, basically, the round explodes way after it passed the aircraft... German HE rounds at least had an impact fuse (maybe including minimal delay due to physics and chemistry), and it set off the round pretty much as it hit.

It is from my memories when I personaly saw that demonstrator made by Oerlikon during my military time, shown probably to give some (unjustified) confidece to the gunners. Was about 25 years ago, so I couldn't "take a photo with my mobile". If I remember correctly, they shot at a range of some 600 or 800 meters, providing that result. If a gunner managed to shoot the "bag" off the tugplanes (usually a PC-9 going at some 500 km/h) cable, it was like winning the Lottery.

 

On a sidenote, I could only shake my head at how long it took to fill a 40 round ammo drum. As the Flab Kan Oe 37 ignited the cartrige while entering the barrel as you fired, you had to grease every single round with a paint brush before tucking it into the drum! Depress the pedal and 10 rounds are gone just like that. A burst that was less than 1.5 sec but felt more like a single shot. The cannon was like a revolver with 4 rounds. We only fired tracers for practise. Although made from steel and having a hard tip, it was surprising how they bent when hitting something hard. Almost like copper bullets. We collected tons of rounds of those from the target range to clean up. I never found broken up bullets, but few bent when they came down hitting rock. They would bend up to 90* off, like a banana.

[MrNoice]

nice now the devs need to fix it...

[ZachariasX]

About the delay of shrapnel production upon impact, the Oerlikon Flab used ammo very similar to the Hispano, also with impact fuze for the HE rounds. That shrapnel is only visibly produced some 20 or 30 cm after impact, could it be that it takes a while for the relatively little amount of explosive to burst a rather strong casing of the bullet? I would guess the demonstrator depicted the normal ocurrence and not an unusually delayed one.

 

In either case, HE rounds work more like a shotgun, not like grenade. Impact fuze will be like you holding your 12 gauge right aganst the target and then pull the trigger. It works staight forward, same as shot. The real world subtleties don't alter that fact.