Take everything written here with a whole sack of salt. I have put hours upon hours of thought into these suggestions, long before ERRANT existed. I also decided long ago that they weren't practical due to being overcomplicated. Also note that my ideas are meant to prioritize a very strange balance between gameplay, realism, and usability. It fails to some extent on every one, especially the last.
Also, any actual numbers given within these spoilers are not recommended--they're only meant to illustrate. My game used dice pools for stats rather than bonuses, and everything else was percentile. Again, overcomplicated.Counting only joules is a very innaccurate method of recording HP. Certain tissue types, such as muscle and fat (obviously), can absorb lots of joules with relatively little damage, while things like your heart, bones, organs--they can't really survive any. A 9mm to the heart is far more lethal than a .50 to the foot. It's also reliably very lethal; get shot within two inches of your heart, and you're just dead. Might last a couple of seconds, but no amount of meth is going to keep you moving ten seconds after your blood has stopped pumping. Even if your muscles have fuel, your brain will shut down in short order if it's not getting bloodflow, and will be significantly reduced in functionality before that--even if you're a very tough individual (source: I used to train Brazilian Jiu-Jitsu and have choked a couple of very fit individuals unconcious, albeit accidentally.)
Your current system would allow a tough man to run at a full sprint for seven entire turns after being shot in the heart by a 7.62x51mm hollow point, with a bit of luck. Assuming turns are about ten seconds, that's a man sprinting without a circulatory for over a minute, just because he's really tough. That seems excessive even for an action movie hero.
A better system would take into account how bullets do damage; in addition to damage, their shape is a significant factor, because muscle tissue can survive a shock, but not being severed. For instance, your standard .45 ball does damage just by being big and fat, which means it cuts a .45"* hole into the person. A .45 HP does increased damage not because it has more energy, but because it sort of flowers outwards to make a wider hole. A rifle (spitzer) bullet does more damage than a .45 not just because it has more energy despite the smaller diameter (the energy would just overpenetrate anyway), but because it yaws inside the body, creating a wound channel as long as the bullet. This is why the 5.7mm is actually a competetive cartridge despite having less energy than other pistol calibers; it yaws, unlike other pistol cartridges. Lastly, the 5.56 does much more damage than its energy would indicate, because it actually shatters inside a human body, creating multiple wound channels each of which has a better chance of hitting something vital.
*Okay, yes, the hole is a bit bigger than that, but still.
Lastly, your system doesn't deal with overpenetration. How much energy does a human absorb from a .50 AP before the round leaves? I doubt it's particularly significant.
If you ask me for a system, I'd make every bullet have a wound modifier, and have a table that's rolled on with categories of wounds. Then, each limb has a list of what each category of wound does to it. Here's an example:
9mm is being fired. It has a wound modifier of -1. I roll 1d6, and get a five, which is modified to four. Checking the wound table, it says that 0 or less only nicks the target, 1-2 causes a minor wound, 3-4 causes a moderate wound, 5-6 causes a major wound, and 7+ causes a critical wound. So my 9mm caused a moderate wound (a .45 would have caused a heavy). I then roll to see which limb I hit, and find that I got the left arm. It says a moderate wound causes significantly degraded function, but not completely degraded function; the foe can continue using his two-handed rifle, but suffers a -1 penalty when shooting it, due to his wound. If I had used a .22 LR, with a wound of -3, he would have suffered a minor wound, which only cause pain, but no functional damage unless another light wound is scored on that arm. If I had used a 9mm HP or a .45, the wound would have been major, and completely disabled use of that arm--it broke a bone. A .50 or something would have easily scored a crit, and the target is now bleeding out in addition to losing their arm.
The torso chart would have organs rather than mere loss of functionality, and would therefore be a more lethal place to be hit. The head would be the worst, with even minor wounds causing negative effective, and moderate wounds likely being near lethal.
END should not give extra hitpoints--just because you are in really good shape doesn't mean you can survive a 7.62 to the heart. Perhaps it could be rolled to reduce the wound by a point or two. Also, it could be used to temporarily ignore the effective of moderate wounds, so the guy I shot in the arm could use his gun with full ability if he rolled well on END.
Armor could work as wound reduction (kevlar), or wound absorption (plates). AP and high-caliber rounds could have equal wounding to ball rounds, but get extra AP points, which are blocked before wound points. However, if any AP points are left when you roll wounds, those AP points are subtracted from wounds, and the round overpenetrates, dealing those subtracted wounds to whatever is behind your target. HP rounds would work the same way, except with negative AP points, so if the enemy has no armor, they suffer extra wounds, but if they have armor, they suffer less.
...Earlier I said "If you ask me for a system...". I wasn't kidding, if you ask me I'll make an entire system like this with all the statistics and charts. Hell, if you want, I'd even be willing to code up an executable which does the calculation and rolls for you. I already have a half-built one from a RTD CQB game I was making years ago (which I abandoned because it was too complicated for anyone aside from me to enjoy).
First problem I see here is that you just list blanket semiauto fire rates. Those vary significantly by person, postition and by caliber. I know several people (and am one myself) who can fire an AR-15 about twice a second with decent accuracy on semiauto, but nobody I know can get anywhere near that with any 7.62, at least not without being prone or having the gun supported. The more you value accuracy, the slower you'll be, and the gap between calibers drops as you increase accuracy, but there's still a difference.
My own preference in a system would be to give all calibers, every gun, and some attachements recoil modifiers. Strength and stances would probably also come in. You add them all together (everthing aside from round recoil should be negative, unless firing CQB guns or pistols or something), and the number you get determines how many rounds can be fired semiauto in a turn, and also how many rounds can be accurately bursted. There should be a maximum number for both which is reached at zero recoil, (or perhaps -10 or something for bursting.)
This way, an M4 gets fewer shots in a burst than an M249, and an M14 gets fewer than both. HOWEVER, a very strong individual could burst fire the M14 with some accuracy, making strength less of a dump stat--currently it's only useful for melee combat and maybe certain actions like lifting, making strength near useless.
Aiming is a problematic system. It's something that's basically required, because you wouldn't expect a special ops soldier to fire six semiauto MP5 shots into a guy at 10m, and hit only his legs and arms. Also, it conflicts with acover system that acts as an aim reduction (which is also what I first tried to do with my cover system)--if you can aim at a guy's head, why would that be harder because the rest of his body is behind cover?
My solution was to make cover be forced aiming, rather than an aim penalty.
Firstly, there's three degrees of aiming, each of which has a set penalty. For the first, you can aim at a specific large body part (torso, legs), and are guaranteed to either hit that body part or miss--hitting other parts on a miss ended up making it ststistically best to always do aimed shots, at least in my system. The second level lets you either specify your wound roll on a large body part, or aim at a specific small body part (head, arm, specific leg, rifle). The last level lets you specify what wound roll you get when hitting a small body part, so you can specify that you want to get a max roll on a headshot, guaranteeing an instakill if you hit (but a hefty chance to fail). It also allows you to shoot a pistol or explosive charge (Note that modern explosives don't generally explode when shot).
Cover works by forcing you to make an aimed roll against a body part that's visible. Half cover forces you to make a 1st degree aimed shot against the enemy's torso. Full cover forces you to make a 2nd degree aimed shot against the head (could be arm too, but head's generally a better target). Things like firing slits are either third degree aiming, or are just impossible to shoot through from a range.
The largest flaw in my system is that aimed shots don't hit other body parts on a miss. Maybe if I went back over it I could find a way to balance that, but honestly I doubt Aigre would want to use my system anyway.
In my system, all guns had two "accuracy bonus" stats. The first was manueverability, which decided how mobile the gun was in CQB situations. The second was actual accuracy, which affected ranged accuracy. For the latter, I ended up giving each gun a specific MOA, and then precalculated chances to miss each target size at 100m increments. That's just too excessive, and I think just continuing to have melee/close/medium/long/extreme is smartest. Due to how accurate modern guns are, and the required granularity to simulate them, it might be best to just give each gun a maximum range. Maybe give them four, one for each degree of aiming.
Without optics, each range should have a base skill penalty. I recommend a bonus for melee range, because it's relatively easy to shoot a head that's only ten meters away. Optics could outright remove range penalties, but I suggest they only reduce them, because holding a gun steady enough to hit a head at 100m is much harder than holdimg it steady enough to hit the same head at 10m.
At CQB ranges, maneuverability is much more important. It shouldn't be used if you can hold your aim on a spot you'll know your enemy will pop up, like a doorway, but it should always be required for aimed shots and moving shots.
For sniping, ranging is important, but there's a lot of ways to ease it. Preranging areas in your FoV is one way, and checking how tall a human is in your scope is another. The entire point of dope sheets is to make it easy to know how the scope needs to be adjusted at which range, so I wouldn't lock snipers to only one range.
I'd recommend that spending a turn to prerange your shot guarantees proper range without a roll, and you can roll intuition to make the shot with a guessed range. Forcing people to always spend a whole turn ranging is jerkish, because a lot happens in a turn in this game.
Spotting should just be a passive intu roll which is automatically made if you aren't busy scoping something. It could get a bonus if you've got a spotting scope, but one shouldn't be needed to even spot at all. A sharp eyed man can see a person walking at 600m, though it's not easy. Also, intuition is already magic, what with being able to tell whether enemies are in a room or floor.
Suppression is different from burst fire. Suppression is only vaugely aimed, and eats more ammo. Both should probably be "scary", but suppression should be more scary.
I suggest suppression not use the shooting skill, aside from basic roll-to-fail stuff; -2 shooting people shouldn't be capable of suppressing without the same risks they suffer when shooting. A gun on full auto is nearly impossible to aim with any real accuracy.
As for the mechanics of suppression, I also suggest it not act as a direct penalty to skill. Instead, it should provoke a mind roll, and if the mind roll is failed the target simply isn't allowed to shoot during their next action. That last bit--"during their next action"--is important. Aliens seem to always take their turn second, so they won't get any benefit if suppression only works during the turn it takes place in; all humans would have already taken their shots.
If the foe has no cover to hide behind, they should be forced to run away, and just skip their next action.
The easiest way to decide how difficult the mind roll for suppression is would be to assign a "scariness" value to each caliber, and then multiply that by how many rounds suppression expends. That way, suppressing with an M240 is scarier than suppressing with a M249, and that's scarier than suppressing with a P90.
I halfway think enemies who are immune (or nearly immune) to the actual bullets, due to armor, shouldn't be immune to suppression. After all, suppression is more about being scary than effective. Then again, if you need heavier weapons to suppress heavier enemies, that's good for gameplay. Also, it prevents players from buying a bunch of American-180s and using those for suppression rather than M249s.
Actual damage from suppression should be the exception, not the rule. You are kinda shooting go kill, so maybe the suppressor could be allowec to roll for one normal burst, but the rest of the shots should hit based purely on luck. I recommend Fate checks for the enemies who passed their mind checks, probably with difficulty based on how many bullets are fired. Enemies who suffer flanking suppression fire should roll multiple times for being hit.
Blind fire is... well, it's stupid, but I suppose rules for it are good because people are stupid. I'd just have the person only be able to fire at locations they've previously seen, and they count as suppressing with -2 shooting skill (without the bonus). So, enemies are hit purely based on Fate, and the shooter has a good chance of shooting their buddy or suppressing the wrong area.
Still writing on the other topics, but I'm on a phone so it's slow... Also, I'm multitasking a lot ATM. Just posting this so others can see and consider it.I think that's every topic? I can't think of what else to talk about. I've almost certainly made lots of mistakes and even more ambiguities, so feel free to ask questions.