Shooting a LOT of Bullets Through a LOT of Folks

[martinl]

Scenario (originally inspired by Peter's blog):

A large block of old school heavy inf, one soldier per hex, 100 hexes wide 100 hexes deep.

A time traveler on their far flank, with effective skill 9 over the entire range of the formation, and a ranged weapon that does 20d at ROF 100 and Rcl 1. She shoots at the first soldier in a line of 100.

Depending on her roll, she gets 0 to 6 hits (call it X1) - the rest of the bullets continue onto the next hex. (Possibly some of the hits as well, if over-penetration is used or target is reduced to -11x HP). IIUC, these bullets perform a ROF (100-X1) attack at skill 9 on the occupant of that hex, and so on until the bullets run out or they reach the end of the line.

In the end, ~1/3 of the guys in the line drop randomly, and the rest are unscathed. Am I doing something wrong here, or is this just a kinds niche GURPS Murphy?

[Blood Legend]

If you set it up like a lab experiment then you'll hit them all in a straight line, dealing with over penetration or what have you. During a war, they wouldn't strictly be in the straightest possible line, and you likely would just drop them at random. More of them are likely to drop closer to the gun.

[Kromm]

Originally Posted by Blood Legend

If you set it up like a lab experiment then you'll hit them all in a straight line, dealing with over penetration or what have you. During a war, they wouldn't strictly be in the straightest possible line, and you likely would just drop them at random. More of them are likely to drop closer to the gun.

Pretty much this. GURPS assumes that targets are highly mobile within their hexes . . . this is why random hit locations can result in hits to everything from head to foot, why even "sure things" like guns at point-blank range require rolls to hit, why people get Dodge rolls against bullets, etc. The actual assumed error is approximately the mesh size – i.e., people are in a hex, plus or minus a yard in any direction, including vertically (someone may be ducking under a friend's weapon, jumping over a stone, etc.). If you can ensure perfect, flawless lines and immobility, don't bother with the combat system, because you aren't in combat. Just roll against Mathematics to set it up and then blast everyone on the line.

[Mathulhu]

This is a well known quirk of the RoF rules when shooting at large targets, I imagine you can find several threads if you google site:forums.sjgames.com rof large target

That in mind effective Skill of 9 and RoF 100 seem odd to me.

You do get the bonus from RoF, up to +7, on the follow up shots as well as the first one. So your initial to hit roll should be higher and get worse as it makes it way through the target.

[lexington]

Originally Posted by martinl

Scenario (originally inspired by Peter's blog):

A large block of old school heavy inf, one soldier per hex, 100 hexes wide 100 hexes deep.

I take it that they're all standing at attention, waiting to be salughtered?

Make a Group Performance (Choreography) roll to getting ten thousand people into position. Each of them needs to make a Will-based Soldier roll to stand at attention for a good length of them. Next an Applied Mathematics roll to make sure the lines are straight. Finally I'd have you make an attack roll at +10 for perfect conditions and -10 for the range to the farthest target, because you have to keep the attack traveling straight along the whole path.

Once you do all that I check to be sure that you're using a laser or something because bullets don't just pass through human bodies without being deflected.

[martinl]

Originally Posted by Blood Legend

If you set it up like a lab experiment then you'll hit them all in a straight line, dealing with over penetration or what have you. During a war, they wouldn't strictly be in the straightest possible line, and you likely would just drop them at random. More of them are likely to drop closer to the gun.

On the other hand, there is unlikely to be ANY clear line of sight through a 100x100 block of soldiers UNLESS they are perfectly ordered AND the shooter is carefully oriented, yet more than half of the bullets are going to go through without hitting anyone. (You could make a case for them going high, I guess, but if you give the shooter skill 22 or something for the first guy 1/3 of the rest still drop.)

More specifically, the last guys in the line effectively have a lot of cover from the guys earlier in the line, but in this case it doesn't matter - they are equally likely to be hit.

In any case, my main concern was that I got the RAW right, which appears to be the case. I'm not really that worried about my contrived scenario happening.

[gilbertocarlos]

An infantry block close packed has more than one guy per hex, if they're really packed you can even see 3 guys on the same hex.
Now, with a very close pack of infantry, you're gonna kill around 100 of them.

[mlangsdorf]

Originally Posted by martinl

Scenario (originally inspired by Peter's blog):
IIUC, these bullets perform a ROF (100-X1) attack at skill 9 on the occupant of that hex, and so on until the bullets run out or they reach the end of the line.

In the end, ~1/3 of the guys in the line drop randomly, and the rest are unscathed. Am I doing something wrong here, or is this just a kinds niche GURPS Murphy?

The cumulative probability of missing a shot, taken against a 9 or less, against 6 different targets in a series is around 1%. Most of the people in that line are going to get hit

Or to make it a manageable example:
10 man sized targets are set up in line when someone shoots a bolt action rifle at them. Hitting a target causes it fall down. The shooter has 10 bullets and isn't a very good shot and never hits at better than a 9 (and for simplicity, he's shooting the first target from 50 yds away, so he never occurs an additional range penalty).

Bullet #1 is a 6, and hits target #1, which falls over.
Bullet #2 is a 12, misses target #2 and continues on to target #3, which it hits with a 9.
Bullet #3 is a 7, hits target #2.
Bullet #4 is a 12, misses target #4, but hits target #5 with a 6.
Bullet #5 is an 8 and hits target #4.
Bullet #6 is a 14 and misses target #6 but hits target #7 with a 7.
Bullet #7 misses target #6 with an 11, #8 with a 16, #9 with a 12, and hits target #10 with a 6.
Bullet #8 misses targets #6 with a 12 and hits target #8 with an 8.
Bullet #9 hits target #6 with an 8.
Bullet #10 misses target #9 with an 11 and target #10 with a 12.
(all dice rolls taken from the d20 dice bag at http://www.d20srd.org/extras/d20dicebag/).

So 10 targets, ten bullets, and only targets 9 and 10 weren't hit. Only 1 bullet missed more than 2 targets.

Basically, firing into a large block like that, most bullets are going to hit something. This is probably not realistic.

Alternately, I'm misreading the rules and there's a -4 penalty for each missed target ahead of the current potential target, but that makes my head hurt.

[Ulzgoroth]

If you fired at a moderate RoF, there would be basically no chance of not having every bullet stopped (or intercepted at least, as 20d bullets don't stop so easily) by somebody.

The trouble is RoF 100. Fire enough bullets in a second (100 might or might not cut it) and you'll overwhelm the bullet-sponging capacity of any set of targets, regardless of whether that makes any physical sense.

The seams on the rapid fire system get really ugly when you use high values of RoF. That's really all I would draw from this, and it isn't a new discovery.

[David Johnston2]

Originally Posted by martinl

Scenario (originally inspired by Peter's blog):

A large block of old school heavy inf, one soldier per hex, 100 hexes wide 100 hexes deep.

A time traveler on their far flank, with effective skill 9 over the entire range of the formation, and a ranged weapon that does 20d at ROF 100 and Rcl 1. She shoots at the first soldier in a line of 100.

Depending on her roll, she gets 0 to 6 hits (call it X1) - the rest of the bullets continue onto the next hex. (Possibly some of the hits as well, if over-penetration is used or target is reduced to -11x HP). IIUC, these bullets perform a ROF (100-X1) attack at skill 9 on the occupant of that hex, and so on until the bullets run out or they reach the end of the line.

In the end, ~1/3 of the guys in the line drop randomly, and the rest are unscathed. Am I doing something wrong here, or is this just a kinds niche GURPS Murphy?

What' you are doing wrong is even rolling for the use of a machine gun against a barn wall. When it's an automatic hit situation, and you don't care where it hits, then you don't roll. Remember that rule about about how you don't need to roll to hit to slit the throat of an unresisting victim?