Shooting at Groups

For your consideration: Here's a new rule I recently drafted for my OED House Rules to handle shooting into large groups of combatants (like into a melee, or an advancing goblin horde). I'm actually kind of delighted by it, but I fear I might be the only person willing to actually implement it.

First, recall a few things about how I run my OD&D. I use a ranged modifier of −1 per 10 feet distance, because that matches a rather large amount of research we've compiled on the blog in the past. Second, I'm working on the continuing project to dial in mass-warfare mechanics well for the Book of War game (hopefully in an upcoming 2nd edition). 

Both of these goals span the man-to-man case and huge-army cases. An aphorism I now use as foundational is: Shooting a man at a hundred yards is impossible, while shooting an army is certain success. (Practically speaking.) Previously in OED I had two different rules to handle the two different cases. The binary switchover has troubled me for a while, and raised a few reasonable questions recently. (I dare say in my head this echoed the conflict in physics between relativity and quantum mechanics.)

So I did some computer simulations and scribbled out some math (I'll spare you that here), and then realized that I could round things off to a rule I could hold easily in my head, and give a smoothly continuous switchover between the two cases. So here's what I just edited into my next draft of the OED rules. First:

Errant Shots

Errant Shots: Fumbled or random attacks into groups are assessed with a d20 roll that ignores attacker skill and range modifiers.

Like the text says, this is a mechanic that I will (and have in the past) used for a few different cases. If someone gets in a fumble situation where they attack themselves or a friend, we invoke this. (Rules where a fumble results in automatic-damage against a heavily armored ally have always ground my gears, or even a normal attack roll as if the fumbler was aiming the perfect attack against a weak spot.) Also a shot against a faraway, large group will trigger this mechanic. (Likewise: close-up an archer should be able to target a vulnerable point on the target, whereas far away this level of skill is impossible.) 

To be clear, in an "errant shot", the attacker's base attack bonus gets ignored. I would want to apply the defender's AC as usual, and I guess also any weapon-vs-armor effect, and magic as well. But to date any time this has happened for me it's just the player rolling a raw d20, and me applying the defender's AC (under the standard Target 20 resolution process). Now consider this:

Shots at Groups

Shots at Groups: Attack rolls (including range, but before AC addition) below 10 miss a man-sized target. Each adjacent man gives a 1 pip chance under 10 to trigger an errant shot against a random target in the group.

As usual, I write that with some curtness in the document. What that means is for a close group of N man-sized combatants, the DM computes 10 − N, and an attack roll from that number up to 10 indicates a shot that completely missed the individual target -- but, close enough to possibly strike someone else nearby (randomly determined, and adjudicated the with the "errant shot" rule above). Some examples:

• Say an archer shoots at an opponent in melee with a single one of their friends. Then a modified attack roll (again: including range but before target AC is considered) of exactly 9 -- no more and no less -- triggers an errant shot against the friend.
• Next, the archer shoots at a squad of 5 men-at-arms approaching angrily. In this case an attack roll of 5-9 results in an errant shot check against a random one of the men.
• Ten goblins are running together down a hallway and the shooter makes an attack. Now an attack roll of 0-9 results in an errant shot.
• A formation of 20 orcs is posted outside a cave. In this case, any modified attack roll from −10 up to 9 triggers an errant shot. 

As you can see, for very large groups at very long range, the mechanic makes it more and more likely that an errant shot against a random target will be invoked. Obviously, the DM should be encouraged to round these numbers off to convenient values -- myself, I'd probably round it to units of 1, 2, 5, 10, 20, etc. I've set it up so the lower bound is found by subtracting from 10 to make it as easy as possible. 

Moreover, the DM should be encouraged to invoke the errant shot rule immediately if it's clear that the shooter simply can't hit an individual man-sized target at the range in question. As a quick rule-of-thumb, if the range penalty is 10 points more than the shooter's fighter level, then they pretty much can't hit anything without a natural 20 (and you should just break to the random shot immediately).

To be completely clear, we're assuming that attack rolls that score 10 or higher are actually on-target, but are fended off by the person's armor if the final resolution (including AC) fails to indicate a hit. Note that this mechanic simulates attack values just a bit below hitting as indicating arrows zipping close by the target (the lower the roll, the further away). And it also allows you to separate out the effect of a critical-miss (natural 1), if you so choose. 

Let's momentarily consider a possibly alternative rule that comes to mind: If a shot doesn't hit, then a natural die-roll in the range from 1-N against N men triggers an errant shot (ignoring natural-1 fumbles momentarily). Seems nice. But the problem here is that it loses visibility of the range in which the shot was actually on-target but stopped by armor (which should be significant for heavily-armored figures). I suppose you could say that a roll of 1 - N (for N men) triggers an errant shot, unless the modified roll is in the range of 10 + AC to 20, in which case it was stopped by the original target's armor. But now you're tracking two different ranges instead of one, and that seems worse to me. (Plus this implies that both very high and very low rolls indicate close-to-the-target shots, while rolls in the middle indicate shots further away, which feels confusing and wrong.) So I would shy away from that alternate proposal.

Aside from all that, another thing that fairly excited me was that the same piece of math that generated this rule also spawned a really nifty rule for handling missile shots in Book of War at targets of unusual size, like solo heroes on the field -- but more on that later.

What do you think of that rule? I've used what I'm calling the "errant shot" mechanic before, but haven't tested the "shots at groups" at the table before -- but I'm pretty confident that would work for me. Would you want to try using that? Anything I could improve in the explanation?