PS: The explosion is at point of impact, thus the forward travelling fragments will not have time to accelerate to any greater speed than what the shell itself was already travelling at before impacting the thing that set off the detonation (In this case, a persons flak jacket).
You are quite correct! However, you are missing the further implication: with no time to start
accelerating, any fragments by definition won't have had any time to start
spreading from the point of impact, either — meaning that the full force of the projectile's forward momentum still hits
in that point. I assume you already know what that implies for the terminal ballistics.
Besides: as I noted earlier, the Bushmaster has a muzzle velocity of 1,100m/s. Say the projectile has slowed down to an even 1km/s at time of impact. At that velocity, the projectile will travel that millimetre in one microsecond — one millionth of a second. That is the time it takes light to travel 300m, or the time of a single 1MHz cycle. It makes no difference how "graze sensitive" a fuse is (it means something different anyway) — I doubt it'll have had time to much more than start to twitch before it's already passed that distance, and then some.
And even
if the fuse ignited the high explosive in the warhead
at the exact moment of contact (which would be physically impossible as the function of the fuse entails motion of mechanical parts and a chain of ignitions, but just for the sake of argument), the ignition wouldn't have been able to propagate even a full centimetre from the fuse through the explosive in that time span. The projectile would have penetrated several millimetres before the warhead was fully ignited.
Factor in the mechanical reaction time of the fuse, and the penetration will be significant.
So, assuming any kind of "soft" (i.e. "not armour plated") target — including a non-reinforced flak jacket — there
will be penetration.
So, there wouldn't be any kinetic energy carried over from the round itself, the kinetic energy would be from the explosion.
Even if there wasn't any penetration — or if we, for the sake of argument, play around with the thought that the projectile has a stand-off fuse that ensures the warhead has detonated fully
just as the trajectory reaches the target — the projectile blowing up wouldn't kill its kinetic energy. The basic principles of physics — in this case, conservation of energy and Newton’s first law — still apply. The projectile's kinetic energy would still be fully transferred to the target. The smaller the area of impact where the energy is concentrated, the greater the penetration, but the energy is still the same.
The kinetic energy from the exploding warhead comes
in addition to, not instead of, this.
So yeah, it's quite a long ...
shot -
- from the 12ga buck or birdshot vs. slug comparison — unless you're postulating that the shotgun's barrel is held about half an inch from the target.
You're still not getting the solid impact. Yes, the fragments that are at the front will keep going straight forward, but the side and rear of the shell will expand outward, meaning both will slow down (rear more so than sides) and spread.
Yes, you are getting (almost) the full kinetic energy on the target, but not as one solid mass.
And it certainly won't pass straight through a human and explode on the other side (at least not one with a flak vest), as you claimed.
And as you most likely know, shape is important for penetration (yes, even for fleshy targets like humans), and the shape of an M792 round isn't very good for penetration after it's split into fragments.
You need to make up your mind. Do the grenade fragments have time to
start accelerating (a pre-requisite for starting to
move apart, in turn a pre-requisite for actually
separating), or do they not?
The correct answer is that they do
not. More about this.
From what I read, it will not provide single-round perforation or incapacitating fragments on any external masonry structural wall. It can create first-round fragments behind wood frame and brick veneer walls.
Now, if your theory of "all that mass and energy is conserved without loss" is true, then that wouldn't be the case. Things start behaving... strange... when you introduce internal explosions to solid objects travelling at high speeds.
Newton's First Law and the principle of conservation of energy (aka. the First Law of Thermodynamics) aren't "theories". They are
laws of nature — absolute and incontrovertible fundamentals of physics. You're facing a bit of an uphill struggle, trying to rewrite them.
The speeds at which these things start getting a bit muddy are orders of magnitude higher than any projectile velocity attainable by terrestrial technology outside of a particle accelerator.
I tried to convey how infinitesimally small a time increment one microsecond is. Clearly I failed. But let's not give up:
In one second, the speed of light covers the length of the Earth's circumference around the equator
seven and a half times.
In one microsecond — the time for a 1km/s projectile to move one millimetre — light barely travels the length of one single Nimitz-class aircraft carrier.
No mechanical system has a reaction time measured in microseconds.
Let's educate a bit on the inner workings of the M758 fuse:
- In flight and armed, it has three activation modes: direct impact, graze impact, and non-impact (ie., self-destruct).
- The self-destruct activates when the projectile has flown so long that the spin and velocity have decayed to a point when centrifugal and wind forces acting on the fuse drop below a certain threshold.
- The detailed operation of the direct impact mode is as follows:
- — Striking a surface causes the fuse's nose probe to be depressed.
- — The nose probe acts on a piston assembly.
- — Overcoming the force of the piston spring, this moves the piston assembly rapidly rearward.
- — The firing pin, being part of the piston assembly, is driven into the detonator.
- — The detonator is ignited.
- — The flame propagates through a channel in the base of the fuse into the body of the projectile.
- — The explosive is ignited. All this takes a little while.
- The activation at low angle or graze impacts has two modes:
- — One is soft targets, where a hit even at a low angle allows the projectile to penetrate into the target so that the nose probe is depressed, as per the above.
- — The other mode is even slower: it is engaged when the projectile hits a hard target at a grazing angle, so that the projectile's flight path is disrupted, activating the self-destruct function.
Reaction times of a "super-quick" fuse are normally measured in tens of milliseconds.
Now, the human eye can't perceive a difference between ten milliseconds or one microsecond — events at either of these time increments will be perceived as instantaneous.
But moving at 1km/s, the difference is that in one microsecond, you cover one millimetre — but in ten milliseconds, you cover
ten metres.
Damn straight it'll pass through a human — flak vest or no — like butter, and explode on the other side. A ceramic or steel reinforced vest might —
might — make a difference, but a Kevlar vest alone will just be that much textile.
To whatever degree the projectile is slowed down won't make a difference in the bigger picture. At a very rough guesstimate, the difference between wearing or not wearing a classic flak jacket is whether the projectile explodes seven metres after exiting your body, or three metres. And let's
not get into the velocity vectors of the fragments at that point...
I mean, don't get me wrong here... I fully stand behind the notion that IRL anyone struck by an M792 round would be truly fucked, flak vest or not.
But this is a game, and unless we want our players to pretty much die from every gun shot wound, we have to have some leeway.
And there is no guarantee that an impact from an M792 round would penetrate a Flak Vest, but IRL it would mess up everything not covered by that Flak Vest anyway, so it doesn't really matter.
(Not to mention the internal damage from the shock of the sheer mass hitting you at that velocity).
Whole separate discussion — how we fudge real-world phenomena to handle play balance and player enjoyment is an issue all its own.
As a side-note, here are some corrections I'd like to make to earlier statements of yours from this thread:
HE projectiles are not; they’re jam packed with high explosive and shrapnel.
The M792 round does not include shrapnel, the outer shell is the shrapnel. You'll find that is the case for many HE projectiles. The filling is usually just explosives.
No. Just ... no.
First, it seems I need to remind of a bit of context that seems to have been very conveniently forgotten. I stated the above quote in response to this assertion:
HE rounds are, for all intents and purposes, hollow.
Which, quite frankly, is arrant nonsense.
Second, in your "correction", again, you need to make up your mind — you manage to contradict yourself in the same sentence: "... does not include shrapnel, the outer shell is the shrapnel". Does the full volume of the grenade include shrapnel, or does it not?
Or is it actually hollow, as you first claimed?
My statement that a HE projectile's volume "is jam packed with explosive and shrapnel" holds true, and I challenge you to contradict it with evidence.
Whether that shrapnel material is integrated in the shell casing or carried as separate ball bearings or whatever, as in larger calibre shells, is completely irrelevant — using the casing as shrapnel is the original way to provide a shrapnel effect from grenades, and it's been used for several centuries.
In whatever form, the shrapnel is part of the projectile. And besides the fuse, between the shrapnel material and the explosive, you will not find any hollow spaces in the projectile.
even if the projectile explodes and fragments completely at the instant of contact without having penetrated even a millimetre
let's not get petty here. We both know that if you fired a BB gun at a Flak Vest, it would most likely penetrate
a millimeter. That's not the point. The point is if it penetrates the vest completely or not.
My point being that it'll penetrate a whole lot more than that. At 1km/s, a mechanical impact fuse is physically incapable of more that
beginning to react before it's passed the length of a human body's thickness.
So, the conclusion can only be that of course a direct hit from a Bushmaster is going to be much, much deadlier than an M82A1 on kinetic energy alone, before even the explosive effect is factored in! Not unlikely, it’ll pass straight through a human and explode on the other side…
This right here is the whole point I'm discussing. No, the shell won't be much deadlier on kinetic energy alone, because a lot of stuff happens to that kinetic energy once a round is split up into fragments and hurled in different directions. Getting hit by one solid projectile weighing 185g is very different to getting hit by a swarm of shrapnel with a total weight of 185g.
And the round wouldn't have begun to split up — the explosive train wouldn't even have been initiated at that point.
But if it
had — on an unprotected body, being hit by a swarm of projectiles with a total mass of 185g travelling at 1km/s is actually worse than being hit by a single 185g projectile travelling at 1km/s.
A
lot worse.
The single projectile has a good chance to overpenetrate, only dumping a fraction of its kinetic energy in the body on the way.
In the swarm, each individual fragment is likely to transfer its full energy into the body, resulting in the body taking the full effect of the 0.1 megajoules of energy hitting it.
Besides: as I noted earlier, the Bushmaster has a muzzle velocity of 1,100m/s. Say the projectile has slowed down to an even 1km/s at time of impact. At that velocity, the projectile will travel that millimetre in one microsecond — one millionth of a second. That is the time it takes light to travel 300m, or the time of a single 1MHz cycle. It makes no difference how "graze sensitive" a fuse is (it means something different anyway) — I doubt it'll have had time to much more than start to twitch before it's already passed that distance, and then some.
You'd be surprised how sensitive they can make fuses these days.
Also, a Flak Vest is pretty thick. We're not talking millimeters here. So does it really matter if the round penetrates a few millimeters before it detonates?
You'd be surprised at the limits the laws of physics impose on things at really, really short time increments.
And indeed — no, we're not talking millimetres here, or even centimetres. We're talking metres.