Thursday, November 15, 2012

Archery Revisited


I've written about refining the D&D archery rules a few times, in regards to indoors ballistics and normalized probabilities (e.g.: here, here, and here). A while ago I again looped back to thinking about them, because a few parts of the prior stuff I've written have started to bother me. Here's the revised rule what I've been using for a while now:


Bows: Bows can be fired every round; slings and crossbows every other round. Indoors, all missile weapons have an effective range of 6"/12"/24" (30/60/120 feet; assume a 10' ceiling). Attacks are +4 at short range, +2 at medium range.

Throwing: A spear, dagger, or hand axe may be thrown up to 12" (60 feet) indoors. These are always treated as long range (no bonus to hit).

Long Distance: High ceilings allow longer bowshots, but these are at -10 to hit individual targets. Shots at great distance outdoors are only effective against armies or the like.



Commentary: The primary issue that drove the change is as follows. Even with the modifications I've suggested in the past, I was still trying to hang on to the hand-wavy system in D&D that you can arbitrarily switch from scales in tens-of-feet (indoors) to scales in tens-of-yards (outdoors) and still use the exact same range modifiers. In retrospect, that's unsustainable, and I'm going to stop using it; different scales simply must recognize different chances to hit. (This would be one of the "distortions" mentioned by Gygax in Dragon #15 [todo: link], and one that most later systems sensibly avoided.)

Let's think about why that was done in the first place. Again, the scale 1" = 10 yards was originally established for historical, mass-combat Chainmail, and in so doing, created realistic scaling for mass figures, movement rates, and bowshots on the tabletop. Later, 1" = 10 feet was used by Arneson in his man-to-man games, and included by Gygax in D&D as the "underworld" scale (Vol-3, p. 8), with 1" = 10 yards maintained as "wilderness" scale (Vol-3, p. 17). But there are two major problems with this retention. First, the 1" = 10 yards scale is less about being outdoors, and more about the mass-combat scale, and so irrelevant for the man-to-man RPG. Second, while it enables a realistic-length bowshot outdoors, it overlooks a colossal and critical fact -- no one in the world can possibly hit a single man at maximum distance with a longbow. Hitting an army in formation, yes, easily so; hitting a single man, no, not even close. And hence this consideration is also irrelevant, and even permitting it is one of the "proud nails" that will irk many about the system for years to come.

So let's agree to abandon the separate scale for outdoors action, and consider some physics for a better rule: Due to the inverse-square-law, if we were being really honest, range categories should work by doubling the distance in each category -- in fact, you see this in a lot of gun-based systems like Boot Hill, Star Frontiers, etc. The D&D system (splitting ranges into equal thirds, linearly) is an outlier in that regard, and just plain incorrect. The best I can figure is that, taking a shot of about 40 yards as a base, every halving or doubling of distance should modify to-hits by about +/-8 on a d20 roll (for example: look at the expert archery table we made before; compare the chances shown at 80 yards and 160 yards; 76%-30% = 46%, i.e., 46%/5% = -9 in that case). Technically this modifier should be applied on our normalized table, but in the meat of the progression it's the same as standard D&D.

Now, it's good to be aware of the correct real-world success chances involved; but at the same time, it's best to take those insights and massage them into easy-to-use, highly memorable mechanics that are convenient at the table. What we've calculated in the past for indoor missile ballistics is a 150' maximum shot for basically any weapon under a 10' ceiling (see here). But I figure it's nice and simple to smooth it out to 120', and so have the range in inches revert back to our familiar multiples-of-three: 6"/12"/24". Also, this happens to line up perfectly for range in inches indicated for the heavy crossbow weapon (the longest in the game). And also the 30' lower limit is the same as that identified in AD&D Unearthed Arcana as "point blank range" (UA, p. 18). And also our bonuses are like those in man-to-man Chainmail/OD&D, except doubled for the conversion factor we agreed on in the past (here). So I think there's a lot in favor of this simple setup.

The scale and the mechanic will be used identically both indoors and out (removing one of the "distortions", as Gygax put it). We observe that single men simply cannot be hit by a bowshot outdoors at hundreds of yards distance. If an indoor area has a very high ceiling (cavern, giant-hall, etc.), then allow a shot perhaps up to 48" (240 feet), but at a massive -10 penalty. For simplicity, the same range rule is used for any missile weapon in the game (presenting something easy to memorize, and reflecting again that range of the weapon has little or no bearing on accuracy against a man-to-man target).


Below are some ideas for optional rules you might also consider using in conjunction with this rule.




Optional -- Other Penalties: The scores above assume best-case conditions. Be sure to apply other penalties for darkness or low-light, cover and obstructions, and possibly high-speed movement lateral to the shooter's field of fire. (See Lakofka article in Dragon #45, for example.)

Optional -- Weapon Variation: If you want to treat various weapons differently for indoor, man-to-man combat, then split ranges in inches into thirds as customary, and apply the +4/+2/+0 bonuses as shown above. For example: a longbow will be 7"/14"/21" (35/70/105 feet). This is not totally accurate, but fairly close, simple, and playable (although not so simple as the unified ranges above).

Optional -- Longer Shots: If you want to permit very long-range shots outdoors against man-size targets, keep in mind that this will be an epic feat achievable only by very high-level warriors. Longer shots can be allowed outdoors at ranges up to 50"/100"/200" (i.e., 250/500/1000 feet, or about 80/160/320 yards), at to-hit penalties of -8/-16/-24, respectively. Of course, the standard maximum range of the missile weapon still applies.

Optional -- Shots at Groups: While I'm thinking about it, here's a possible rule for shots at groups of size N. Step 1: Identify a target for the shot by random method. Step 2: Roll d20 to hit, but as long as the natural die-roll is less than or equal to 4×log2N, then re-roll any miss. See here for the exact upper bound: N=1:0, 2:4, 4:8, 8:12. (The basic observation here, again based on the inverse-square-law, is that each doubling of range category is balanced by each quadrupling of area/people in the group, i.e., +/-8 to hit. Therefore each doubling of people should be effectively half this, or +4. I don't actually do this, but perhaps you'd like to try it.)

6 comments:

  1. Maybe firing at a mass of men requires the mass combat rules instead of man-to-man rules.

    We need to have a rule that can apply equally well to a bunch of men spaced out 5' apart from each other and men in a block with no gaps.

    How about this:

    An archer firing at Short range can choose a single man-size target. At Medium range you have to choose a 10' square (4 men-sized, 8 if you consider it to be a cube). At Long range you choose a 20' square (four 10' squares or 16 men).

    The Short range attack is a hit or a miss; he chose who he was firing at.

    The Medium range attack could hit any of those four squares. Some squares will be empty, some full. The DM should roll d4 and count across from the upper left corner, then to the left side of the next row down and across, etc.

    So the counting would look like
    1 2
    3 4

    This will make more sense in Long, which is a 4x4 square. You need a d16 or else roll d20 and reroll results 17-20. This counting would look like this

    1 2 3 4
    5 6 7 8
    9 10 11 12
    13 14 15 16

    (The comment box might remove extra spaces or switch me to a non-monospaced font, so just realize this made a lot more visual sense to me when I typed it)

    When you figure out who the attack went to, the attack roll applies to that target.

    You could come up with another way to diffuse the targeting, but this multiplies the number of possible targets by 4 each time (technically 8 if you include airspace). It also accounts for large creatures, ships, buildings, etc. being easier to hit than small men.

    A magic item "of accuracy" could downgrade the range to the next lower, making the attack roll easier and the selection of targets more precise.

    This prevents long-range firing into melee safely, unless you manage to pick out a "safe shot zone" where there are no friends.

    You could also do this with siege weapons.

    Personally, the rule I use for grenade-like missile scatter and shot scatter for indirect fire is this:

    d8 for direction. 1=North, count clockwise.
    dX for distance in 5' increments. I like dX-Y to allow for the chance of 0 scatter.

    d4-2 x 5' for Medium gives a 20' diameter circle of possible targets, and d8-2 x 5' for Long gives a 60' circle.

    Again, this generally prevents someone from hitting a single target at Medium or Long range, but it's not impossible. It also makes it easier to hit a packed group than a loose group than a single man.

    If you give shot scatter for long range, you might want to rethink having an attack roll penalty. Does the attack roll penalty mean the arrow is slower and less likely to deal damage at the end of its flight? Is it because the archer can't really aim for a vulnerable spot past a certain range? I always thought of the range penalty as the reduced chance to hit a single specific target. But as you say, hitting a unit of men or even an actual barn is easy to do at long ranges. That's well simulated by the shot scatter and I don't think we need a penalty to hit.

    Would be interesting to see the actual chance to hit a man-sized target given a few different methods for determining shot scatter, and compare to range penalties and the real-world test results, and see if they can be brought together.

    At that point, you're sacrificing ease of use (the penalty to hit is an EASY way to handle this while the shot scatter takes longer and has system vulnerabilities) for adaptability to multiple situations (in which the shot scatter method is superior).

    Maybe you could use shot scatter if there's something else interesting to hit in the area, or the range penalty if there's just a shot against a lone thing. But that's probably not worth the trouble.

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  2. The bonuses for short and medium range are pretty intense; they make a short bow at 6" a plate-cracker equal to an OED warhammer.

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    1. You're right of course, and sometimes when I come back to this my intuition is that it needs to be tuned down. But I come back to the pros of (a) a +1/+2 situational modifier practically not worth the time to remember, (b) physically pretty realistic, (c) in line with the AD&D modifier scale, and (d) a big incentive for melee fighters to close with an archer and stop their firing. It's definitely a good thing to be aware of.

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    2. And I guess I should point out that it's also in scale with the +2 I give for axes vs. chain/plate, and +4 for a mace et. al. vs. plate.

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    3. Yeah, I'm with you on all points there.

      I keep wondering about putting penalties on medium and long range rather than bonuses on short and medium, but that does seem over-punitive.

      Reviewing my latest rules notes, I see that my prior conclusion was to just ignore range increments and have a flat effective range (well, two, one for man-to-man scale and one for mass scale). Simpler, for sure, but I'm not convinced it's better.

      One thing I'm currently contemplating is using your universal range but giving long bows the bonus you give to axes and (heavy) crossbows the bonus you give to maces. That would let thieves and clerics have basic missiles and give fighters a significant advantage with advanced weaponry.

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