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Psienesis wrote:
They don't carry half a dozen kinds of ammunition for a squad-automatic... at best, you've got 3. Standard ball, tracer, and maybe some AP.

Sorry if it wasn't apparent. I was referring to different calibre, not type of round within calibre. FM 3-06.11 Combined Arms Operations in Urban Terrain's table generally only refers to standard NATO ball, with a couple of separate referenced to use of AP.

He's going to eyeball it, give it a burst and see what happens. If he sees daylight? He's going to keep shooting. If he doesn't? He's going to keep shooting to keep their heads down while the RTO calls for fire or the mortar team gets the tube set up.

I wasn't arguing that small arms fire was an efficient or recommended way to demolish structures. The above said manual is discussing the relative effort required to penetrate a structure (once).

By "reinforced concrete" I assume they mean with rebar within poured block? For the physics of this, that's irrelevant reinforcement, and might, in fact, make the wall more brittle to incoming fire, given the way rebar and poured block work.

I assume the same. I don't recall the text elaborating that much, however. Just 'reinforced concrete.'

That said... a 5.56mm round is most likely not going to leave a quarter-inch depression in the wall... especially if it runs into one of those reinforced rebar bits (if it doesn't, then the use of reinforcement in this context needs clarifying, as there are lots of ways to reinforce concrete!). It's a fast round, and highly lethal to soft targets, but, copper jacket or no, makes little difference to a concrete wall.

Standard M855 NATO with steel penetrator.

The round hasn't got the mass to dig a quarter of an inch into the wall with every shot. This is also going to be highly dependent on the age of the concrete. The older it gets, the more its cured... and, after a certain age, it actually starts to get more brittle, which may permit a 5.56 round to do that. Upshot.... there's too many variables in this equation to take such a statement at face value. In addition to myself having served in the Army, my father was a concrete mason. I spent far too many summers working for him to not know a bit about the varieties and vagaries of concrete. There's dozens and dozens of different kinds of concrete... densities, mixtures, additives, etc... simply too many to say that "concrete" stops X number of Y kinds of bullets.

Well, I did say 'average.' I am familiar enough with tank armour penetration mechanics to know numbers are estimates that may be wildly off in a given situation. Obviously, the manual wouldn't even try to be that detailed, nor would it make sense for it to.

Having been on both the giving and receiving end of fire behind 24" of sandbags... it requires a whole hell of a lot more bullets than 220 to tear it apart... you could probably burn two or three belts from from a 60 and still have plenty of sandbags looking back at you. Sure, it's not going to be pretty after that, but it should still be functional... assuming you placed your bags properly, and didn't half-ass it like legos.

Again, I didn't say tear apart, only penetrate once. The contention of the manual is that this many rounds, fired accurately at a close range (100m) with good shot grouping, will succeed in getting one final round through. You keep using adjectives like "tear apart' or such, which is both vague, and different from the manual's term or intent. If you have experience that actually contradicts the wording and meaning contained in the manual, fine. I can accept that. Books have been wrong before. But so far, you seem to be saying something else.

Of course, if they are projecting the force of one round on a sandbag and then determining the energy required to tear through them and from that determining the multiplicative results... well, that might be accurate, from a technical standpoint, but it's not something you will ever see in reality, since no one is going to be able to put 220 rounds dead on target on the exact same point of the sandbag wall. You know we stack a layer of sandbags six to eight deep on top of foxholes to defend from mortar fire, right? Works pretty good, too, provided the material supporting your overhead cover doesn't give away. Then you just get buried alive.

Obviously, I don't know the method use to derive the table. As the table specifies 100m or less, we can assume all the rounds are hitting within either a 13" (SAW) or 4"(M16A2) circle or less, since the wall isn't moving. The manual does not differentiate by weapon, only calibre, however.

19 dreadnoughts will most certainly tear through a concrete wall

That, at least, is certain.

Psienesis wrote:Here's the thing about cover and weapons:

If cover, let's say a wall of sandbags, can stop bullets from 1 assault rifle, it can stop bullets from 1000 assault rifles.

Eighteen inches of packed earth can stop 5.56mm rounds indefinitely. Doesn't matter how many M16s you shoot at that wall of packed earth, it's never going to go away.

If we extrapolate that lasguns work on the same principle, we get the same results. If one lasgun cannot shoot through a concrete wall, then 1000 of them aren't going to do it, either. Cover simply doesn't work that way... at least, not until you're dealing with weapons actually piercing it. When you have cover being carried away/blown away by the rounds hitting it, then you can wear it away with massed fire. If not? Then it will never happen.

1.
That's a generalisation.
Enough bullets will penetrate 18" of earth, the issue is that "enough" is a lot.
If you punch holes in the sandbags the sand will fall out, do that enough and you've got no wall.

Similar thing with an earth bank, you might think that the bund in the butts of the ranges is an impenetrable barrier but they actually require quite a lot of maintenance.

2.
That extrapolation is invalid.
A bullet goes into the material, moving it out of the way and stops there. Some of it falls out.
A Lasgun pulse hits a target and uses its energy to vaporise some of the material, there is now less material.
Enough hits will remove enough material to penetrate.


The limb removal thing is a big DEPENDS.
Old soft lead muzzle loaders ripped limbs off all the time. It is about energy transfer.
Different bullets transfer energy in different ways depending on many things including how much energy they have due to range travelled.

The same bullet hitting your shin will do different damage than if it hits your calf.

I have seen a limb removed by an AK round but it struck the ball of the shoulder directly and destroyed the whole assembly removing the bulk of the limb, it was only held on by some skin and connective tissue.
Guy died in the wokka.
I have also seen a .50 rip off an opfor's leg and buttock by hitting the hip joint in a similar way.


So that means that the Lasgun is equivalent to a 7.62x39, a .50BMG and a musket ball.
So, no direct equivalent at all then.


Basically the Lasgun is used because of the benefits it presents to the Imperium.
It is cheap, reliable, easy to manufacture, recoilless, accurate (due to no ballistic trajectory to worry about and having no recoil) long ranged (not covered in the game but a laser's range is only limited by the curvature of the earth, pushing through air isn't all that hard), requires no ammunition and does cumulative damage.

Bullets suck. Thinking about it - they should be assault 2 or 3, they have no recoil so what's stopping you shooting while you run?
Surely it must be easier to shoot a Lasgun on the move than a shotgun?

Meh.

Also, as I am now reminded.... a Field Manual (FM) from pretty much any modern military is a slightly-toned-down real-world equivalent of the Infantryman's Uplifting Primer... and they used to be *much* worse!

Some of our (as in, US Army) FMs and other training materials from the Korean War era and post-War occupation of Europe.... wow! The propaganda just fairly *dripped* off the pages. The more recent editions are much more subtle, as the intelligence and worldliness of the average soldier has greatly increased in the past few decades (a scary thought, indeed...), but are still filled with much supposition, opinion and... well, let's just call it "flavor", from the military brass that writes these things.

Tech Manuals (TMs) are much less flavorful. They tend to be pretty dry, and simply discuss how a given item works, how to fix it on the spot, and what it's used for, and how to go about making it fulfill its primary role.

Bullets suck. Thinking about it - they should be assault 2 or 3, they have no recoil so what's stopping you shooting while you run?
Surely it must be easier to shoot a Lasgun on the move than a shotgun?

Have always wondered this, myself. Even Abnett describes the kick of lasguns in the Tanith novels. Larkin's long-las supposedly kicks like a mule. I have to ask "why?". It's just a bolt of light...

If I had to guess, it's from the superheated air leaving the barrel due to expanding so fast. But that wouldn't provide THAT much kick, would it?

Maybe the force of the flashlight leaving the barrel causes the kick, but in all homnesty i would not expect them to kick, But then what about meltas and plasma?

I would suspect not, Melissa. Yes, there are particles of light in a laser and, yes, they have to be accelerated somehow to be focused into a lethal laser... but I cannot imagine them requiring so much effort as to be physically discomforting to an adult human.

For meltas... I believe the chemicals used in generating a melta-beam are under pressure, so there might be some "pushback" from them leaving the muzzle of the weapon... though, again, nothing like a firehose or something, but probably a noticeable push.

Plasma? They fire by magnetic acceleration, I would imagine the only kick they should have is from thermal variation as the charge leaves the muzzle. This might actually cause a significant recoil, given the wild variance in heat between the round and the surrounding air, and the fact that the super-heated air in/around the barrel is going to be quickly supplanted by the cooler, denser air from the surroundings, via convection current. Might be a fairly noticeable kick, at least for an unaugmented human.

Moving and firing is not very hard. Moving and firing accurately is the tricky thing. Recoil or not, your lack of a stable firing base makes for tricky shooting at any sort of range. at 25m hitting a man sized target on the move is not difficult, as long as you are moving slow enough to aim. I see no problem with Assault 2 or 3, as long as BS dropped to compensate for squeezing of second rate pot shots on the move.

I've seen a video of a laser being used to propel a replica space-ship thingy very high into the air. It was supposed to be a model for how a laser could actually be used as a propulsion device. The model was just tin-foil iirc but still.

If we're talking about a laser with enough power to actually blow someone's arm off then I suppose it's possible it would have some kick for the arm on the other end too.

What everyone forgets is as weapons have evolved as have Armour. Who knows mabye Ork plates are Admatinium infused with secret sauce and the 6+ SV is to represent them hitting it.

Melissia wrote:If I had to guess, it's from the superheated air leaving the barrel due to expanding so fast. But that wouldn't provide THAT much kick, would it?

Could be that, however there doesn't need to be an open ended barrel on a laser, technically the objective lens could just be the end of the weapon, there would be no structure to trap the air and therefore minimal thrust from its venting.

beef wrote:Maybe the force of the flashlight leaving the barrel causes the kick, but in all homnesty i would not expect them to kick, But then what about meltas and plasma?

Melta, not sure, I thought the basic function of a melta is like an open ended fusion reactor. If it is just heat coming out of the end then that is (technically) the same as light in that it is an electromagnetic emission.
If you are suggesting that something with mass comes out of a melta gun then there is a bit of a problem.
The material in a fusion reactor has a name.
It is plasma.

Plasma guns would have recoil, it is using a magnetic coil to accelerate plasma, the plasma has mass, accelerating the plasma will cause a recoil force.

The red bit is addressed by the answer below.

Psienesis wrote:I would suspect not, Melissa. Yes, there are particles of light in a laser and, yes, they have to be accelerated somehow to be focused into a lethal laser... but I cannot imagine them requiring so much effort as to be physically discomforting to an adult human.

For meltas... I believe the chemicals used in generating a melta-beam are under pressure, so there might be some "pushback" from them leaving the muzzle of the weapon... though, again, nothing like a firehose or something, but probably a noticeable push.

Plasma? They fire by magnetic acceleration, I would imagine the only kick they should have is from thermal variation as the charge leaves the muzzle. This might actually cause a significant recoil, given the wild variance in heat between the round and the surrounding air, and the fact that the super-heated air in/around the barrel is going to be quickly supplanted by the cooler, denser air from the surroundings, via convection current. Might be a fairly noticeable kick, at least for an unaugmented human.

Bit of a mess of physics here.
All wrong too I'm afraid.
Working backwards:

Plasma, you are right on how it would work but that would definitely cause a recoil effect. Convection almost irrelevant.

Melta, (as above) depends how it works. If it is a beam of heat (high intensity infra-red electromagnetic radiation) then it is basically a lasgun with a different "colour" of light. If it is actually shooting something out then there will be significant recoil, very much like a fire hose but the stuff coming out would be plasma and that would make it a Plasma gun.

This might be the eternal dilemma of the clueless fluff writer though, you never know.


Lasers.
Whew, that is a lot of fail in that sentence.
"Particles of light" is a bit of a misnomer, they are known a photons but they are not really particles, at basic levels of education the teachers will call them that to help explain some of the behaviour of photons, photons also behave like waves though.
Basically (not true but I simply cannot explain the actual answer here):
Photons have no mass, therefore projecting them cannot cause a recoil effect.
Photons are already travelling at the speed of light and therefore cannot be accelerated since it is not possible to go faster (the current tachyon furore will die down, trust me) than light.
Lasers do not accelerate light they amplify it, they do that by starting with a small number of photons and using them to cause certain chemicals to release more photons, those photons release more photons and so on and so on until there are an awful lot of photons, that is a laser.
The light in a Laser is the exact opposite of focussed, "focussed laser" is an oxymoron.

Put shortly there is no way a laser can cause recoil no matter how much power it has.

KamikazeCanuck wrote:I've seen a video of a laser being used to propel a replica space-ship thingy very high into the air. It was supposed to be a model for how a laser could actually be used as a propulsion device. The model was just tin-foil iirc but still.

If we're talking about a laser with enough power to actually blow someone's arm off then I suppose it's possible it would have some kick for the arm on the other end too.

1. I've seen that, it was really cool. However the laser was not propelling the thing. It was a spinning disc or reflective material that focussed the light from a laser into a chamber in the bottom of the disc.
The laser light would then superheat the air in the bottom of the disc. The air would explode, causing thrust.
The laser was then turned off and the air moved back into the area in the bottom of the disc, the laser was then switched back on causing another explosion.
Basically the pulsed laser caused the air to explode and the exploding air provided the thrust.

As I recall the biggest problem they had was that the reflective material the disc was constructed of wasn't reflective enough, some of the laser light was absorbed by the disc which got extremely hot and melted, the next laser pulse hit a melted blob instead of a mirror and blew it to pieces.

2. You are thinking of Newton's 3rd law, that the energy causing the arm to be blown off must first be applied to the burst of light by some kind of process that causes recoil.
It doesn't.
There is an energy exchange but it is electrical energy creating a laser beam, no mechanical force at all.


If anyone has any other questions about the physics of these things feel free to ask, I am not a professor or anything but I have a decent grasp of the subject.

One last disclaimer, I am not trying to come across as superior - sorry if it seems that way.

OK, well do photons not have mass? The often used sci-fi concept of solar-sails, for example, is theoretically possible isn't it?

Photons do have mass, yes.... though it is of an insignificant amount in a Earth-equal gravity well. Solar sails work... in space, where everything is weightless. They're useless in a gravity well. So while the photons of a laser may generate recoil, this would (scientifically speaking) only matter in a gravity-free environment, which is not the normal fighting arena of the IG and equivalent forces.

But, hey, it's 40K. Our flashlights go pew-bang! and have recoil. /shrug

This laser, which is the weakest one in 40k, is still unimaginably stronger than anything in real life. I think that a laser with that kind of strength could have a kickback. Don't forget we're talking about 19 megaTHULES!

Yeah, but laser is basically concentrated light and light have no mass. The only kick you can got is from the contraption that generate las shot in Lasgun.

Melissia wrote:

Pyriel- wrote:I'd say no.
Concrete is heat resistant

Not as much as people think...

Its pretty good, which is why its used as fire protection. Its essentially made of rocks with a melting point of a couple of thousand degC. If you have 100mm thick slab and expose one side it to about 1000°C then it will take about an hour for a significant amount of heat to penetrate to the unexposed side (cf. Eurocode 2 part 1-2).

Reinforcement in concrete will always help it resist loading as it picks up the tensile forces that plain concrete is not terribly good at resisting.

It can have problems with spalling when heated rapidly which might help a laser weapon penetrate, but it would still take quite a bit of time and may not actually be any different from the impact damage it would take from bullets. also if you're expecting spalling you can change the mix to make it much less susceptible to the problem, i.e. fibre reinforcement or controlling the voids that form in the mix.

Solar sails do not catch photons they generate thrust from solar wind which is a high speed plasma of electrons and protons, both of those have mass and can therefore impart thrust.

Please get the mass of a photon out of your mind in this context, megathule energy levels or not the mass of a photon is irrelevant.
A laser does not accelerate the photons and therefore since it is not imparting any force to them they do not impart any force to it.

Therefore - no recoil.

A photon is generated by an electron dropping down from one shell to another, that is stimulated by another photon interacting with the atom.

rob-or-ross wrote:Solar sails do not catch photons they generate thrust from solar wind which is a high speed plasma of electrons and protons, both of those have mass and can therefore impart thrust.

Please get the mass of a photon out of your mind in this context, megathule energy levels or not the mass of a photon is irrelevant.
A laser does not accelerate the photons and therefore since it is not imparting any force to them they do not impart any force to it.

Therefore - no recoil.

A photon is generated by an electron dropping down from one shell to another, that is stimulated by another photon interacting with the atom.

Except for those solar sails which are driven by. . . lasers. Yes, that is a thing, which has been done. All electromagnetic radiation, including light, exerts pressure; see the Maxwell equations. That also very, very strongly implies that photons do, in fact, have mass.

I'll just leave these here:

http://bbs.stardestroyer.net/viewtopic.php?f=4&t=123079]Grand 40k sticky

http://bbs.stardestroyer.net/viewforum.php?f=4&sid=cda00edc00ea32042e031d3cb2a0aee5
Scroll down and check other pages to find 40k analysis.

Here is one of the analysis that can be found on the second link:
http://bbs.stardestroyer.net/viewtopic.php?f=4&t=150910
It talks about Lasguns.

@Cpl Renzov - Good links.

Thank you, I hadn't seen those before.

@BeRzErKeR - Yes, I did mention in one of my posts in the three threads that are discussing this at the moment that I was simplifying.
The science is by no means complete on that subject but it would seem that a photon could have a mass in the order of 10E-69 Kg.
Which is negligible when talking about a recoil force from a hand held weapon.

Also, we have the issue about whether the laser is actually accelerating the photons.
If it isn't accelerating the photon then there will be no reactive force.

If it is accelerating the photon then in the tube the photons will be stimulated going in all directions giving a net thrust of zero.

That means that the only unbalanced force would be the difference between the full mirror and the partial mirror.
How much force does a laser impart while bouncing off a mirror?

How much laser energy would there have to be before that unbalanced force generated a perceivable recoil force to an armoured human in earth equivalent gravity?

Would that energy match the damage caused by a Lasgun in the fluff?

I think in this context we can discard the mass of a photon.


On the solar sail thing, I was wrong, I read up a bit more and it seems particulate impact is in the order of a thousandth of the photon pressure.

That photon pressure is still in the order of 5 millionths of a newton per square meter.
Meaning you'd need 200,000 square meters of sail to generate a newton of thrust.

Quite fascinating but also not really capable of generating a recoil force that will be felt by a human.

No, you're right; a laser wouldn't generate any recoil, because it isn't accelerating anything. The photons are already moving at lightspeed, a laser simply, for lack of a better word, organizes them. However, it probably would have a kinetic effect on whatever the beam hit. How big a kinetic effect? Damned if I know. Likely very small, though.

As to the solar sail thing, you'll note that that force is approximately doubled if the light is reflected rather than absorbed. You do need a big damn sail to generate much acceleration, but it's doable. In fact, it's been done!

Yeah.

I with they'd just invent the Star Wars hyperdrive already.

The kinetic energy imparted on the target by the bolt would be negligible but it would be supplemented by the steam and vaporised flesh/armour blasting out of the wound like a rocket motor.

Yet, people get knocked down, spun round, tossed back and every other sort of thing as if they had been shot by Hollywood Bullets when shot by a lasgun in the fluff.

Hmm, actually, that might be the best explanation for all of this stuff pertaining to the humble lasgun: the Hollywood-Cool Effect.

Why does a lasgun have recoil? Because gritty warriors in combat with bucking, kicking weapons fits the Hollywood-Cool effect.

Why does someone shot with a lasgun get thrown back ten feet? Hollywood-Cool Effect.

Why do lasguns never run out of ammo until it's dramatically important? Hollywood-Cool Effect.

Yes. Now you're getting there. The fluff writers know all about futuristic combat. They've seen Robocop.

I've never heard of penetrating two feet of concrete.. if it exists it would probably be extrapolated from a calc someone with too much time on their hands did, and it may or may not be valid depending on the assumptions and variables involved. The closest I've heard of to penetrating any sort of building material would be from battlezone Cityfight where it was said Laspistols could shoot through brick walls and still be lethal.

Could a lasgun penetrate concrete? If its a highly focused series of pulses designed to blast its way (through simulating miniature explosions -yes you can do that and there are several ways to do it) you can drill a hole through. Such weapons would likely be of the sort that drill a hole straight through the target (as opposed to burning them or blowing their heads apart or blowing limbs off).

Psienesis wrote:Also, as I am now reminded.... a Field Manual (FM) from pretty much any modern military is a slightly-toned-down real-world equivalent of the Infantryman's Uplifting Primer... and they used to be *much* worse!

Some of our (as in, US Army) FMs and other training materials from the Korean War era and post-War occupation of Europe.... wow! The propaganda just fairly *dripped* off the pages. The more recent editions are much more subtle, as the intelligence and worldliness of the average soldier has greatly increased in the past few decades (a scary thought, indeed...), but are still filled with much supposition, opinion and... well, let's just call it "flavor", from the military brass that writes these things.

Ah, yes. I have the Department of Morale's 1943 manual German Psychological Warfare, and the Handbook on German Forces. I am aware of the trend. Those books make for some comical reading, to be sure. But the penetration info in the FM in question seems to be, from the text, there as an actual rule of thumb for things like shooting a loophole out of a wall, or neutralising a dug in sniper or mg with sustained fire. And okay, sure, they used to tell soldiers that MG.42s were 'inaccurate" and easy to dodge by sprinting. I am well aware the US military says and does some silly things. I spent some time in cammies. Still, don't you think they tested those values at all? It's not like it is hard to find some concrete to shoot at, or to get somebody to shoot at it. I really have to think that somebody was actually curious enough to test it, however cursorily. Some Infantry battalion COs actually care that much, you know.

Moving on from there: This website http://www.industrial-lasers.com/articles/print/volume-20/issue-9/features/processing-rock.html discusses (briefly) industrial lasers cutting sandstone. It specifies a 3.2kW laser 1" in diameter melting a hole at around 2"/minute, or about .84mm/second.

This http://www.dae.gov.in/ni/nisep02/catlaser.htm discusses a 20kW laser of 47*45mm melting through 5mm of concrete in a 100 nanosecond pulse. (If I have read the article correctly.) Not that that helps us convert Megathules...or gives us the beam diameter or pulse duration of an Imperial lasgun...

Still, don't you think they tested those values at all? It's not like it is hard to find some concrete to shoot at, or to get somebody to shoot at it. I really have to think that somebody was actually curious enough to test it, however cursorily. Some Infantry battalion COs actually care that much, you know.

Yes, but this gets back into what I was saying earlier about different kinds of concrete having different strengths/weaknesses/compositions and so forth and so on. Not exactly sure that an Infantry CO is going to have both the desire to test the FM as well as the appropriate knowledge of various kinds of concrete and such. I mean, of course it's possible, it just seems like it would take a lot of alignments of stars and such to have such a thing happen.

It just makes the concrete mason's apprentice in me want to say "Yeah? What kind of rock?" when things get to talking about doing this, that and the other impressively destructive thing to "concrete".

Well, I have never intended to argue that they made a comprehensive survey of concrete for the FM, or that the figures given wouldn't be variable with differing types of the material or conditions. Nor do I have any reason to doubt your knowledge of concrete.

I only argue that it seems reasonable, due to the ease of testing, that they actually did tests at some time, against some kind of concrete, likewise the other materials listed, to obtain the figures, whether that was of whatever kind of concrete was at hand, or was of a type they rightly or wrongly considered 'typical.'

While I grant that the military is sometimes backwards enough to not bother testing something that simple, it seems to me that it is just as plausible to assume the figures are approximately true against some kind of concrete, in some condition of weather and age, and then consider what kind of concrete that most likely was, and how other types and conditions would effect that, as a benchmark against which to consider our laser question here.

I admit, I didn't read the thread, but lets put it this way:

An Atlas-F nuclear missile silo, which is designed to be undamaged from a direct nuclear attack, has 3 foot (~1 meter) thick concrete walls. I kind of doubt that a lasgun can punch through TWICE that.

EDIT: In any reasonable timeframe of an attack.

Shrike325 wrote:I admit, I didn't read the thread, but lets put it this way:

An Atlas-F nuclear missile silo, which is designed to be undamaged from a direct nuclear attack, has 3 foot (~1 meter) thick concrete walls. I kind of doubt that a lasgun can punch through TWICE that.

EDIT: In any reasonable timeframe of an attack.

You're argument is invalidated by the future.

Shrike325 wrote:I admit, I didn't read the thread, but lets put it this way:

An Atlas-F nuclear missile silo, which is designed to be undamaged from a direct nuclear attack, has 3 foot (~1 meter) thick concrete walls. I kind of doubt that a lasgun can punch through TWICE that.

EDIT: In any reasonable timeframe of an attack.

My understanding of nuclear missile silos is that 'withstand nuclear attack' actually meant a miss in the near vicinity. To the best of my knowledge, no silos are actually capable of withstanding a direct hit. But they didn't have to be. Such was the difficulty of targeting over the distances involved, adverse atmospheric, heat and vibrational effects on the targeting systems, and the (relatively) small size of the silos from above, that it was thought very few (20%?) would receive direct hits. The rest only had to survive a warhead impacting within a few hundred, or maybe 10s of metres. However, IIRC, anything under something like 70m was considered to be probably lost.

Since you didn't read the thread, let me encapsulate where we are on that, relative to your statement: I think we pretty much agree that no one is going to burn through several feet of concrete with a pulse or two. The question is, can a large number of hits, as say, a squad or platoon concentrating their fire, or a soldier expending several energy packs burn through?