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Due to the current situation me and my group decided to try something new for our first online-session. We agreed on a post-apocalyptic, post-modern setting in a Metro2033-style. This presents me with a few new challanges. While I can bend most of our current rules to work semi-normal in a modern adventure, a big problem is handling automatic weapons.

I already have something in mind for semi-automatic guns or rifles with single- or burst-fire mode, but I haven't found nothing for full-auto or tap-fire weapons. I discussed the issue with my players already, but we haven't found a solution everyone is happy with.

Our requirements for a usable "Automatic-Weapon-System" are:

  • It must be easy to execute, which means it should take as few dice rolls as possible with few-to-no calculations. We don't want the game to pause for a few minutes to calculate the results each time our machine-gunner fires blindly into the crowd.
  • It needs to be properly balanced. Machine guns are supposed to be lethal, but need a drawback.
  • It must work for both single and multiple targets (I'll come back to that later)
  • It should be random. This point contradicts with my first point, but a few players - and I myself - would like to have 'spraying' be as unpredictable as possible. The hard part is make something hard to predict, but easy to calculate.

I should probably mention our homebrewed combat system I'd like to use:

We use an "Action-Point Table" (which is actually an old score-counter board from Carcasonne). Each Action costs Actions-Points. Each time you use Action Points your maker on the board moves up. It is always the turn of the player with the lowest number. (So if Player 1 is on square 4 and Player 2 is on Square 7, it's Player 1's turn. He spends 4 Action Points on moving, now he has 8 and P2 has 7 ... and so on).

Feel free to ignore this system, if you have a great idea without using it. I just think it might create some room for imagination (also I'd like to build on it, since I've written it^^).

Here are a few things we thought about, but didn't quite like or finish:

  • You roll x times to decide your accuracy, then draw a cone on the map based on it and split the damage to all targets in the cone. Each target gets damage based on (ammount of bullets/squares within the cone next to it). => hard to draw a cone, not random
  • Each weapon has a 'spray pattern'. You pick a target and then roll once for your accuracy. Based on a 'recoil table' you determin how many bullets hit your target, if there is another target within the 'spray pattern', you roll again for the remaining bullets. => didn't really sound fun
  • You fire x bullets per action point (based on weapon), you roll once to determine how many bullets hit then for each hit once to determine whom it hit => sounds like a lot of rolling
  • You pick a target, the game-master can give a hidden modifier for anyone close nearby. You roll for each bullet fired, then reveal the hidden modifier, to see if any missed bullet has hit one of the bystanders => lot of rolling, calculation and I'd like to avoid making things too dependent on the GM
  • The player picks a group he wants to target, then rolls x dice based on bullets fired at once. There is an open modifier based on how large/tight the group is. Damage is split among the group. => not really random, basically a lame AOE.

I also need meaningfull differences between burst fire (a built-in burst mode to fire a fixed amount a bullets each time you pull the trigger), tap-fire (shortly press the trigger for bursts of a few bullets) and spray (pull the trigger and hold for as long as you can)

I also already have looked up some post-apocalyptic RPGs, but none of them seems to have a very fun approach to automatic weapons. If you know one with a fun rule you can cite, that might supply what we need.

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  • \$\begingroup\$ Do you have rules for handling recoil on firearms? If so, consider applying them so that burst fire has more recoil than single-shot, and "spray" has more than burst. \$\endgroup\$ – Jeff Zeitlin Apr 6 '20 at 23:35
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    \$\begingroup\$ To what extent do you want to simulate reality and to what extent do you want something that's fun or cinematic? From all that I've read, in real combat situations fully automatic fire is extremely impractical for actually killing enemies, since the muzzle rise will make accuracy almost impossible beyond the first few shots. It's most useful as a tool for suppressing the enemy and preventing them from acting, and even then you really want to be using a heavy, mounted gun to limit the recoil. \$\endgroup\$ – Kyle Doyle Apr 6 '20 at 23:45
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    \$\begingroup\$ "Now I'd like to keep this question as nonspecific as possible, so any answer is suitable for many others but me." - Semi-related meta: Should I use a narrow system tag, or use a broader tag? Essentially, you should focus on asking the question in a way that will yield answers relevant to your actual problem, rather than artificially broadening the question. Don't feel compelled to make the question nonspecific unless you yourself are interested in nonspecific answers. :) \$\endgroup\$ – V2Blast Apr 6 '20 at 23:48
  • \$\begingroup\$ @KyleDoyle Some years ago the Marines went with the mod to the M-16 that changed the "auto" selector to "three round burst" for that very reason. (well, at least in part). I think the Army did the same. \$\endgroup\$ – KorvinStarmast Apr 7 '20 at 12:49
  • \$\begingroup\$ I have cleaned up the prose in this question - there were a lot of small grammatical, usage, and spelling errors. I also removed that point V2 Blast mentioned for two reasons. (1) it adds no value to your problem statement and (2) it does indeed render this question as too broad. Please review the edit and make sure the tone and messages has been retained. \$\endgroup\$ – KorvinStarmast Apr 7 '20 at 13:53
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D20 Modern (from the D&D 3.0 era) that might help you here

In it automatic weapons shoot on autofire. Autofire targets a 10ft radius. You make an attack roll against AC 10 to hit the area you are aiming for. If it succeeds all creatures in the radius need to make a DC 15 reflex save or take the weapon's damage. Autofire uses 10 bullets.

With the burst fire feat, you can instead fire a burst of 5 bullets at a single target. You get a -4 on the attack roll but deal +2 dice of damage. If the weapon has a 3-round burst setting, you can instead only use 3 bulelts to get the same benefit. A similar system might work for you (with or without requiring a feat for burst fire).

In this system for autofire it doesn't say what happens if you miss the AC 10 area you are aiming for (I believe you just waste the 10 bullets as they spray off into the air or past your targets and off the map). What might be interesting is another rule in d20 Modern which is for thrown explosives like grenades. You target a 5 foot square, and you automatically hit if it is in one range increment. You simply roll 1d4 to determine which corner the grenade lands in. If it is further, you need to hit AC10. If you hit, the grenade lands in the targeted square and you roll 1d4 for corner, but if you miss, it lands in a corner of a nearby square in a random direction (for the second range increment roll a d8, if a third range increment a d12 and there are diagrams for where it lands).

I would suggest that if you want randomness for autofire you can combine these ideas. Have autofire target a 10ft sqaure, and if you miss roll a die (or two dice, one for direction one for distance if you want) to determine where to place the actual 10ft sqaure. If you don't want every weapon to use the same number of bullets or the shape of its autofire to be the same, you can easily write rules for that too. If you want this randomness to apply more often, increase the ac of the sqaure, or add modifiers for range, cover, visibility, etc, so that full auto is less likely to hit the area that is intended.

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  • \$\begingroup\$ In your first paragraph, you refer to DC 10 to hit and in your third paragraph, you refer to AC 10 to hit. Is that intentional? I also reformatted you lead in to make a title out of it, sort of a "bottom line up front attention grabber" ... and FWIW I like your answer. \$\endgroup\$ – KorvinStarmast Apr 7 '20 at 12:54
  • \$\begingroup\$ No it should say AC in both \$\endgroup\$ – Andrew A DeMarco Apr 7 '20 at 15:43
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Despite lacking the tag indicating thus, this question's body seems to indicate it's a very fundamental game-design question, one focusing on core principles, not even getting into specific dice mechanics, so I will address those fundamental principles, assuming you'll work on the exact implementation at some future stage. I think like other homebrew, this will almost inevitably have to become an iterative process, requiring additional questions once you decide which of the solution-paths to accept or reject.

Ease of Execution

This heavily biases the selection of acceptable mechanics towards those where the attacker only makes a single, modified, roll per target (or even per turn spend autofiring!), with some modifiers and maybe a very simple lookup for the number of potential hits, while the defenders may be making their own defence rolls or apply a static defence (I'm unsure whether your system uses a rolled or static defence calculation).

Balance

The main drawbacks of autofire can be summarised as inefficiency. This inefficiency is twofold. First, there is the matter of spending more ammo per hit scored, on average - significantly more. Second, there is the matter that all the rounds after the first in a burst do not benefit from the time spent aiming before the burst, but they do benefit from the (less precise) walking-the-burst effect.

Odds of hitting a small target at long range with a decently-recoiling weapon more than once are actually not that good, so if you want to enable a chance of scoring multiple hits at all, this should only happen on very good rolls.

So if going for a single-roll resolution against single targets, and wishing simplicity, you may want to have weapons provide a small bonus to hit dependent on the amount of bullets spent; the more easily controllable the weapon (LASERs being the most controllable, something like a helicopter minigun carried by a robot barely strong enough to wield it the least controllable), the better the ratio of the bonus to the amount of bullets spent, capped based on rate of fire.

This does allow differentiating well between single, tap, burst and long-duration auto fire. This inevitably requires a couple of additional parameters for weapon stats, but it doesn't require table lookups unless you want to get fancy. More controllable weapons are usually ones that have weaker calibres, better ergonomics, additional heavy and/or expensive stabilising accessories etc. - that should help you balance them.

Multiple Targets

Here is where it gets tricky. First of all, there two ways in which multiple targets may be threatened during autofire: walking a burst through several targets, and being within the general zone of suppressive or other autofire.

Walking the burst should probably be treated as hitting a target multiple times, with an additional reduction of efficiency due to traverse through the path between intended targets. Easy way to solve that is to take the attack modifiers for targeting the hardest target (even if it's not the first target!), make a roll, then distribute the successful hits evenly between all the targets and all target-sized empty spaces between targets.

So if we think that a typical person is a 'one-metre target', and there's two metres of distance between the two intended targets, assume that the first person gets hit with ¼ of the successful hits, the second with the other ¼, and that the two metres of empty space eat up the remaining ½ of the ammunition. Simplified, but playable. Even simpler if you have hexes or squares on your map, so you can just count them to figure out the amount of area that 'consumes' wasted bullets.

Being within a threatened area is different. It happens both when an area is attacked by general suppression fire, and to any collateral (not necessarily intended) targets near an intended target. The odds of being hit are pretty low though, given that the same number of bullets tends to be spread either around a rather big area, or around an area involving only the intended targets. The psychological effect is probably more worth modelling than the individual chance to be hit. Furthermore, while evasive movement has a certain effect on targeted fire, it basically doesn't do anything (unless you're faster than bullets or precognitive!) against zone fire, because one has no way to predict which spots within the beaten zone to evade.

So if you're set on modelling the more random hits during autofire should probably be involve (1) willpower/courage/discipline checks to keep doing what you want to be doing without disruption (such as a desire to hide behind the nearest cover) and (2) either a small chance of suffering a hit based on ratio of bullets to the zone covered (the effect of skill will be absent or negligible under many circumstances, so long as the shooter is neither completely untrained nor superhumanly good with guns), or (if the system requires a defence roll) by defence rolls at a big bonus dependent on the aforementioned ratio.

Again, if you use squares or hexes on a map, it makes counting those area-to-bullet ratios easier.

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I have at least 2 contending Systems. The issue is that in both armor reduces damage. But either of them could be imported into your system.

  • I recommend against adapting a D&D or one of it's derivates since they do not do that. IIRC, this was done to speed up combat but it causes quite a number of artifacts in game handling.
  • That armor does not reduce damage (only makes hitting harder) is perhaps my biggest issue with those systems where firearms are in play

Systems that may work for your situation.

Shadowrun

If you want modern weapons, you can hardly go wrong with a look at it. They have been dealing with Autofire since 1st Edition. Autofire is de facto the default, rather then the exception. If you do not know what else to pick and nothing is forcing you into small arms, a SMG is rarely a bad idea.

It seperates the "Fire" action into: Single-Shot, Semi-Auto shot, (short) Burst, Long Burst, Semi-Auto Burst, Full-Auto and supression. The whole Recoil Mechanic exists to make "persistent Autofire" less viable and give weapons something extra to diversify on (recoil reduction).

What throwing more bullets down the line:

  • it applies a Defense Modifier. Since defense is rolling directly against the attack and net sucesses can increase daamge, that is a combination hit chance increase and damage increase
  • aside from eating ammunition like a troll eating soyburgers, it is also building up recoil quickly
  • Supression is a odd case. It is a Cone-shaped Area of Effect attack, that applies a Roll penalty to all enemies even if they stay in cover. Everyone not in cover also has a chance to be hit by a bullet, based on Reaction+Luck
  • Visibility and Recoil penalize the Attacker, but cover or running target buffs the defender and is thus countered by Autofire

HERO System

This System has two ways of dealing with Autofire Weapons.

  1. The Heroic way with Autofire Skills and weapon proficiencies is way more detailed.
  2. The Superheroic way is simpler.

Heroic way:

  • Autofire Skill and Weapon Proficiencies are a thing
  • If you fire against single targets, good sucess means additional hits. With each ones damage being rolled seperately.
  • There is a optional extension rule to roll a single piece of damage, but with increased damage. Wich is situationally usefull with the way armor, stunning and knockdown work.
  • Alternatively you can use Sprayfire to effectively "draw a line with bullets", allowing you to hit multiple enemies
  • in turn Action Point Costs - usually the main limitor for attacks - do not really apply in Heroic

Superheroic way:

  • You got the single target autofire or can go full area of effect. None of that detailed stuff like Sprayfire. If you want to hit more then 1, use Multiple Attack or Area of Effect
  • As Area of Effect and Autofire afect Action Point Costs (with AP limits matering) and Damage Class Calculations, the per-hit damage of those attacks is relevantly less. And as armor reduces damage - and is especially high in superheroic - that can make it less effect to useless against some targets

Those two rules are not technically fixed to Heroic or Superheroic, but they are clearly designed for either of them. "Corssing the streams" is possible, but I would not advise it.

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    \$\begingroup\$ The question is tagged "homebrew" and makes no mention of D&D that I can see. So why do you start with two paragraphs of talking about D&D, when there's no indication that the OP's homebrew system is D&D-based? \$\endgroup\$ – Dave Sherohman Apr 7 '20 at 11:49
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    \$\begingroup\$ @DaveSherohman As the Rule System (basis) was not specified, it is possible to be a D&D derivate. And if it is, that would basically invalidate my entire post. So 2 Paragraphs at the start of my post showing the limittions of my answer? It seems highly appropirate. \$\endgroup\$ – Christopher Apr 7 '20 at 13:40
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    \$\begingroup\$ @KorvinStarmast Thank you. I am really, really bad at that part. \$\endgroup\$ – Christopher Apr 7 '20 at 16:52
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    \$\begingroup\$ Glad to be of assistance, thanks for the answer. :) \$\endgroup\$ – KorvinStarmast Apr 7 '20 at 17:55

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