Is the intent to make this information available to the player?

If so: consider simplifying this.

If not: then, why put so much effort towards making it that detailed?

This information is available if the player has a high enough score in the relevant skill to determine the stats of an object.

I can't imagine the point of this. The only reason to make complex calculations is to force a player to make decisions in a single fight. Otherwise everyone will just memorize a wiki made by some math crafters and all this work will be for nothing. In theory you might use this in a system when you can customize weapons and armor, ie, the enemy prefers lasers for w/e reason so you create an armor to minimize lazer damage catching them off guard.

You *can* customize weapons and armour. Not only that, in some of these games you can make it yourself if you have the time. You can increase protection against a single type, or in a single manner. Although DD is pretty consistent and is hard to increase without changing materials or armour types, the others can be increased individually and it's not hard to do. The reason you need two additional types is to provide the player a choice, and more importantly a meaningful one. DR and RE might be more or less effective depending on damage type, the amount of damage and the penetration. It's up to the player to determine which will be more effective for their purposes.

I want preparation to be important to the player. More specifically, I want it to be the best way for a player to gain an advantage in the game. I want to encourage muchkins, and turn every player into one. The player should be spending any time they aren't fighting or managing aftermath of fights planning their build, optimizing their loadout and customizing their equipment to gain the greatest possible advantage in the next fight. Added complexity within the system, if it is done right, can lead to characters making some interesting and creative character builds and being rewarded for it with greater successes. This becomes especially important in team games, where entire guilds do this in a coordinated manner. I thoroughly enjoy this kind of customization, and using it to encourage coordination and teamwork within guilds just makes sense to me.

You're ruleset is ridiculously over-complicated. Having to check 9 different stats (6 defensive and 3 offensive) just to determine the amount of damage dealt by a bullet to one layer of armor is ludicrous. With two armor layers and two damage types per weapon, there are 21 different stats that can affect how much damage a person takes from any given attack. It really feels like complexity for complexity's sake, which is rarely, if ever, the origin of an enjoyable ruleset.

If this was a tabletop, you'd have a point. But it's not. A computer is checking all of these, not the player. And all the player needs to know in the heat of the moment is "alright, this isn't working. I need a bigger gun, or I need to hit harder." You can work fine doing none of this math. You don't need to be a bio-medical or weapons engineer to know how to kill somebody. It's just better to know all of this, and if you do you can achieve greater effect than if you didn't know any of it.

One detail, which maybe I didn't understand correctly, seems seriously wrong: damage to consecutive aligned targets is reduced only by armour DR of earlier targets. Wouldn't a larger discount, equivalent to treating other targets as armour with significant damage reduction, be more natural? Targets should have a "damage capacity", treated as DR from the point of view of the bullet. For example: a soft bullet through one eye ricochets inside the skull, doing full damage to one person only with no chance of hitting someone else, because its damage (slightly reduced by sunglasses DR) is less than the DR rating of a head. Another example: a rifle bullet that does X damage and can go through N unarmoured persons implies that each victim absorbs X/N damage, and after exiting N people the bullet has negligible energy.

One detail, which maybe I didn't understand correctly, ...

Well you're right about one thing.

...seems seriously wrong: damage to consecutive aligned targets is reduced only by armour DR of earlier targets.

No, no it isn't. It's reduced by all three. First, DD reduces penetration. While this isn't damage per se, it is a serious factor in determining the damage to later targets. Second, both DR and RE permanently reduce damage that a weapon deals. For instance, a bullet that (after penetration) encounters a DR of 10 and an RE of 10%, for instance, WILL do 10 points and an additional 10% less.

Wouldn't a larger discount, equivalent to treating other targets as armour with significant damage reduction, be more natural?

That's already how it is. Every single target's DD, DR and RE counts against a projectile. Every time a bullet passes through somebody it loses penetration and dumps energy, as well as usually losing damage.

Targets should have a "damage capacity", treated as DR from the point of view of the bullet.

Or, they could just have regular DR, which they already do.

For example: a soft bullet through one eye ricochets inside the skull, ...

No, no it doesn't. The only structure in the skull that can stop bullets is the glabella, especially since the skull provides less than half the resistance from the inside. In order to ricochet inside the skull, a bullet would have to enter the skull at an angle shallow enough to barely glance off the inside, and at this angle it wouldn't penetrate the skull in the first place. The odds of a bullet finding a spot weak enough to penetrate at such an angle is astronomical, and even if it did, it's unlikely it would maintain such an angle because every time an object passes through another object its trajectory changes. Further, the most a bullet can possibly ricochet inside a skull is one time. After that, it'll be at a perfect angle to pass through the skull on the next impact. Even if this didn't happen, brain tissue is a lot stronger and denser than people give it credit for, especially towards the back of the skull, and the bullet simply wouldn't have the momentum to bounce more than once. You are talking about a long chain of glaring improbabilities followed by a physical impossibility.

...doing full damage to one person only with no chance of hitting someone else, because its damage (slightly reduced by sunglasses DR) is less than the DR rating of a head.

The DD, DR and RE of a pair of sunglasses would be negligible. #9 could go through it, and that's saying something because #9 has been known to be stopped by the thicker portions of human skin. No bullet present in-game is going to be significantly weakened by a pair of sunglasses.

Another example: a rifle bullet that does X damage and can go through N unarmoured persons implies that each victim absorbs X/N damage, and after exiting N people the bullet has negligible energy.

NO. No it does NOT. Damage is NOT energy. Do you know what kinetic energy does in a human body, in any quantity that could be delivered via bullet? It causes light bruising. Human tissue is really, really good at absorbing kinetic energy. It is elastic, it stretches a great deal before any damage is done, and it's only the tissue too stiff or too thin to stretch (adipose and capillaries, respectively) that are damaged. Most of a bullet's damage comes from it's momentum, and the form it takes is the gaping hole the bullet leaves in a human body. The size of that hole is determined by the size of the bullet, and the depth is determined by its momentum, not its energy. The closest to energy-based damage actually taken is the bruising, which doesn't really matter unless the tissue the bullet passes through is unusually stiff, and the next closest is the exit wound, which doesn't reach vitals and in fact is usually barely deeper than the skin, so it is not a significant contributing factor either. Energy does NOT equal damage.

I'm confused. How are lasers dealing "concussive" damage?

How do they have any kinetic component at all?

Otherwise seems like a really cool system. It does seem a wee bit overcomplicated with possible room for some simplification, but like you said the computer is doing all the heavy lifting so....

Take care!

I'm confused. How are lasers dealing "concussive" damage?

How do they have any kinetic component at all?

Why yes, yes they do. It's called an "explosion."

Otherwise seems like a really cool system. It does seem a wee bit overcomplicated with possible room for some simplification, but like you said the computer is doing all the heavy lifting so....

Take care!

If I was going to simplify it at all, it'd be by removing RE. Because as it is, it really doesn't do anything significant.

Not to be nitpicky or anything, but how are you imagining lasers? I can't conceive of an implementation having any kind of explosion/K.E. at all. If you're thinking something like what appeared to be a plasma spitting repeater from Terminator (i.e., the future/flashback where a T800 infiltrates a human base, dogs start barking, and it whips out a 2 handed rifle and begins to unload on everything) then maybe I can see where you get the explosion part, but that would more fall under some kind of plasma weapon than an actual laser. I.e., the humans fired back with lasers in that same flashback. And even in that case the "explosion" was simply the super heated plasma expanding on contact and creating a crack/pop. Not something I would imagine as an actual explosion, per se.

Why wouldn't lasers simply have tons of pierce?

Not to be nitpicky or anything, but how are you imagining lasers? I can't conceive of an implementation having any kind of explosion/K.E. at all. If you're thinking something like what appeared to be a plasma spitting repeater from Terminator (i.e., the future/flashback where a T800 infiltrates a human base, dogs start barking, and it whips out a 2 handed rifle and begins to unload on everything) then maybe I can see where you get the explosion part, but that would more fall under some kind of plasma weapon than an actual laser. I.e., the humans fired back with lasers in that same flashback. And even in that case the "explosion" was simply the super heated plasma expanding on contact and creating a crack/pop. Not something I would imagine as an actual explosion, per se.

Why wouldn't lasers simply have tons of pierce?

That is about as incredibly wrong as anything you could have ever possibly said. Any time you dump a large amount of any kind of energy into a small area in a short period of time, you get an explosion. And yes, this includes thermal energy. This is a pulse laser. It has a fire time of one millisecond, and a high yield. If you put 300,000 joules onto a circle one centimetre in diametre in a time that short, you will get an explosion with roughly the same force of a small grenade.