Engagement of Area Targets with Fully Automatic Fire

[sir_pudding]

From here.

Originally Posted by Ulzgoroth

However, yes, a +4 would be considered appropriate if it's deemed a 'non-combat' situation.

While the "non-combat +4" isn't supported in the rules as written it seems to have near-rule status on the forums; that doesn't make it an actual rule. However what would apply in the "Set up a machine gun with Tripod and T&E (Traverse and Elevation), zero it, and fire at the broadside of a barn" scenario are the +3 for known distance, and the max bonus for extra time, also bonuses for favorable wind and lighting (why wouldn't you get these bonuses, you have all the time in the world). You can easily get +10 or more this way.

I'd also ask what that has to do with the relation between RoF, attack bonus, hits, and outside factors.

For every +Rcl in bonuses that's one less shot that misses. I don't see the issue.

Originally Posted by Ulzgoroth

Oookay, then I'd have to disagree. If that were the case, there shouldn't be an SM bonus to hit.

If you are aiming center of mass, a larger object is easier to hit, simply because it's easier to see and to get sight picture.

When you attack an object, you're attacking the object as a whole unless otherwise specified.

I disagree. The hit location rules seem to assume a center-of-mass point target.

Originally Posted by Ulzgoroth

By all means. But in GURPS, if you're firing a vulcan at an aircraft carrier from any more than a carrier-length away (to guarantee 'close stationary' isn't a factor) from the ship it's essentially impossible to not miss with the vast majority of your fire. Even if you're firing it from a stabilized ground-based turret mount.

This scenario is utterly absurd, why would anyone ever do this? A machine gun or even an autocannon can't be expected to do anything to an aircraft carrier's hull. You attack giant capital ships with anti-shipping torpedoes (and Soviet torpedoes designed to kill United States Navy supercarriers had some of the largest payloads of any conventional weapons ever deployed) or Surface to Surface missiles; not direct fire conventional guns. The rules are meant to be realistic, I don't see why we'd expect them to handle completely absurd situations.

However, lets address it anyway. Unfortunately I've lent my High Tech out, so I'm going to have to use the generic stats from Basic Set for weapons.

The United States Ship Nimitz is an elongated box 1,092 feet long giving a SM of +15.

Assume the Nimitz is sitting at anchor 600 yds away from a pier. A High Mobility Multipurpose Vehicle with a mounted Heavy Machine Gun [like a M2 .50 caliber (that's a .5 Browning in the Commonwealth)] drives up, stops, aims for three turns, and opens fire on the Nimitz. Assuming a Gunner skill of of 15:
15 (skill)+6 (Acc) +2 (additional aim) +1 (Tracer/Ball mix) +1 [All Out Attack (Determined)] +1 (Rapid Fire) +1 (Braced) +15 (SM), -16 (Range)= 26

On average roll of 10 all 8 shots hit. Where is the problem? Even if the gunner rolls a 14 for example and misses with one shot, it's not implausible that the shot hits low striking the end of the pier or the water.

[Ulzgoroth]

I've got a notional rules-mod.

Instead of adding one hit per rcl margin of success, add a variable number depending on the effective target size. To determine this number, add the SM and range modifier of the target, multiply by 2, and add N (an undetermined constant), then look up the length associated to that SM.

N should be set so that the rule matches the GURPS rule for a man-sized target at the range that rule is tuned for.


The idea is that all else being equal, a target will take a number of hits proportional to the arc that it fills. Though it over-corrects somewhat since you'll also get a larger margin of success shooting at a larger arc.

Originally Posted by sir_pudding

While the "non-combat +4" isn't supported in the RAW it seems to have near-RAW status on the forums; that doesn't make it an actual rule. However what would apply in the "Set up a machine gun with Tripod and T&E (Traverse and Elevation), zero it, and fire at the broadside of a barn" scenario are the +3 for known distance, and the max bonus for extra time, also bonuses for favorable wind and lighting (why wouldn't you get these bonuses, you have all the time in the world). You can easily get +10 or more this way.

I actually thought that +4 for non-combat shooting was pretty well supported by the plinking box, though I've never had a satisfactory definition of 'non-combat'. The rest of the +10, though, seems more circumstantial.

Originally Posted by sir_pudding

For every +Rcl in bonuses that's one less shot that misses. I don't see the issue.

That doesn't answer the question I'm trying to ask at all. I don't know how to clarify it, though.

Originally Posted by sir_pudding

If you are aiming center of mass, a larger object is easier to hit, simply because it's easier to see and to get sight picture.

The question isn't whether you're aiming for center mass. Aiming for center mass is probably the best way to hit with as many rounds as possible! The question is whether the attack roll is ignoring hits more than a yard from the aimpoint, or including all hits on the target.

Originally Posted by sir_pudding

I disagree. The hit location rules seem to assume a center-of-mass point target.

I don't see it, so far. Noting the following definition of 'point target' here:

Originally Posted by sir_pudding

A point target is no more than a meter across, like a person or window. An area target is bigger, like a fireteam or a wall.

Originally Posted by sir_pudding

This scenario is utterly absurd, why would anyone ever do this? A machine gun or even an autocannon can't be expected to do anything to an aircraft carrier's hull. You attack giant capital ships with anti-shipping torpedoes (and Soviet torpedoes designed to kill United States Navy supercarriers had some of the largest payloads of any conventional weapons ever deployed) or Surface to Surface missiles; not direct fire conventional guns. The rules are meant to be realistic, I don't see why we'd expect them to handle completely absurd situations.

Shooting an autocannon at an aircraft carrier may be unlikely. That's entirely beside the point. The example is not important. The behavior of automatic weapons against large or close targets is.

There's probably another point to be made about how shooting an aircraft carrier with an autocannon would be far too effective in GURPS, but that's a different thread again.

Originally Posted by sir_pudding

However, lets address it anyway. Unfortunately I've lent my High Tech out, so I'm going to have to use the generic stats from Basic Set for weapons.

The United States Ship Nimitz is an elongated box 1,092 feet long giving a SM of +15.

Assume the Nimitz is sitting at anchor 600 yds away from a pier. A High Mobility Multipurpose Vehicle with a mounted Heavy Machine Gun [like a M2 .50 caliber (that's a .5 Browning in the Commonwealth)] drives up, stops, aims for three turns, and opens fire on the Nimitz. Assuming a Gunner skill of of 15:
15 (skill)+6 (Acc) +2 (additional aim) +1 (Tracer/Ball mix) +1 [All Out Attack (Determined)] +1 (Rapid Fire) +1 (Braced) +15 (SM), -16 (Range)= 26

On average roll of 10 all 8 shots hit. Where is the problem? Even if the gunner rolls a 14 for example and misses with one shot, it's not implausible that the shot hits low striking the end of the pier or the water.

Yeah, that works out to a reasonable result. But you're using a weapon with a relatively low rate of fire, which lets you get by in this scenario.

Should you really need the entire Nimitz as a target if you want to score ~80% hits at 600 yards?

[Kuroshima]

Originally Posted by Ulzgoroth

I've got a notional rules-mod.

Instead of adding one hit per rcl margin of success, add a variable number depending on the effective target size. To determine this number, add the SM and range modifier of the target, multiply by 2, and add N (an undetermined constant), then look up the length associated to that SM.

N should be set so that the rule matches the GURPS rule for a man-sized target at the range that rule is tuned for.


The idea is that all else being equal, a target will take a number of hits proportional to the arc that it fills. Though it over-corrects somewhat since you'll also get a larger margin of success shooting at a larger arc.

That's how things work right now. It's the same to shoot a 2 yard target at 2 yards, than it is to shoot a 3 yard target at 3 yards, etc etc. since the SM and the range scales are the same.

[Ulzgoroth]

Originally Posted by Kuroshima

That's how things work right now. It's the same to shoot a 2 yard target at 2 yards, than it is to shoot a 3 yard target at 3 yards, etc etc. since the SM and the range scales are the same.

No and yes.

It's the same to shoot a 2 yard target at 2 yards as a 5 yard target at 5 yards. But that doesn't mean they're taking hits proportional to their arc (not quite the right word, since I mean effective target area). To check that, you have to try shooting the 5 yard target at 2 yards. And if you do that, under RAW, you'll hit with one extra shot (assuming rcl 2 weapon as usual), not ~4 times as many.

[Kuroshima]

Originally Posted by Ulzgoroth

No and yes.

It's the same to shoot a 2 yard target at 2 yards as a 5 yard target at 5 yards. But that doesn't mean they're taking hits proportional to their arc (not quite the right word, since I mean effective target area). To check that, you have to try shooting the 5 yard target at 2 yards. And if you do that, under RAW, you'll hit with one extra shot (assuming rcl 2 weapon as usual), not ~4 times as many.

Let's see:
Assume that a circular target, 1 yard radius (SM+2), situated at 10 yards (-4 range penalty).
The view cone has an aperture 2𝛉=2*tan⁻1(1/10)=0.199337305 radians ⇔ 𝛉=0.099668652
The solid angle is 𝛀=2𝛑(1-cos(𝛉/2))=0.007800405 steradians

Now, let's assume a 10 yard radius (SM+8) target, situated at 100 yards (-10 range penalty), its obvious to see that 𝛉 (the aperture angle) has the same exact value, thus 𝛀 (the solid angle) has the same exact value.

That's the beauty of exponential scales such as the Size/Range table.

[Ulzgoroth]

Originally Posted by Kuroshima

Let's see:
Assume that a circular target, 1 yard radius (SM+2), situated at 10 yards (-4 range penalty).
The view cone has an aperture 2𝛉=2*tan⁻1(1/10)=0.199337305 radians ⇔ 𝛉=0.099668652
The solid angle is 𝛀=2𝛑(1-cos(𝛉/2))=0.007800405 steradians

Now, let's assume a 10 yard radius (SM+8) target, situated at 100 yards (-10 range penalty), its obvious to see that 𝛉 (the aperture angle) has the same exact value, thus 𝛀 (the solid angle) has the same exact value.

That's the beauty of exponential scales such as the Size/Range table.

Two targets that occupy the same arc are attacked the same (aside from 1/2D and max range effects). I'm well aware of this. That's a precursor to what I'm saying, not a refutation.

I'm saying that attacks on targets of different arcs should have a particular relationship.

[Kuroshima]

Originally Posted by Ulzgoroth

Two targets that occupy the same arc are attacked the same (aside from 1/2D and max range effects). I'm well aware of this. That's a precursor to what I'm saying, not a refutation.

I'm saying that attacks on targets of different arcs should have a particular relationship.

Maybe they should, but such relationship should be proportional to the solid angle, and it's not a calculation for the faint hearted. It's definitively not a naive linear relationship with the linear dimension (and thus with SM). It's not even a quadratic relationship with it. I could wing up a spreadsheet that made the calculations for you, but still, it would be cumbersome to use at the table.

[Ulzgoroth]

Originally Posted by Kuroshima

Maybe they should, but such relationship should be proportional to the solid angle, and it's not a calculation for the faint hearted. It's definitively not a naive linear relationship with the linear dimension (and thus with SM). It's not even a quadratic relationship with it. I could wing up a spreadsheet that made the calculations for you, but still, it would be cumbersome to use at the table.

Solid angle! Thanks for that, I couldn't find the term...

Well, two things there. I'm not sure why you'd think that shots are going to be distributed evenly in terms of solid angle, in particular...though they won't really be distributed evenly in the target plane either. Regardless, the square of linear dimension/range is close to proportional to the solid angle for 'small' targets...not very bad even up to a 45 degree target (it's twice a 26.6 degree target, rather than a 22.5 degree target).

So if solid angle is a better basis than area/range^2, I'm pretty happy with using the latter for an approximation.

[sir_pudding]

Originally Posted by Ulzgoroth

I actually thought that +4 for non-combat shooting was pretty well supported by the plinking box, though I've never had a satisfactory definition of 'non-combat'. The rest of the +10, though, seems more circumstantial.

You are going to have to quote it then. I don't recall anything that explicitly gives +4 for non-combat shooting. I do recall an explicit +3 for known distance, though. Again I'll remind you that there's no reason you can't just aim for the max time allowed for precision aiming as well.

The question isn't whether you're aiming for center mass. Aiming for center mass is probably the best way to hit with as many rounds as possible! The question is whether the attack roll is ignoring hits more than a yard from the aimpoint, or including all hits on the target.

Kromm says:

Originally Posted by Kromm

Actually, the game does assume a point target. Shots at anything big enough to have "walls" are assumed to be at a 10-square-foot area; see p. B558. If you exceed the HP in that area, you cause a breach at that one point. For huge targets like buildings and aircraft carriers, the other hits simply don't contribute to the breach. They certainly still count as hits against the wrong target, which here can be crew on deck, protruding antennas, and anything else that isn't the primary 10-square-foot target. The rules don't say that if you fire a machine gun at a truck, all the bullets that "miss" magically bend around the truck; they just say that they don't contribute to chewing up the truck's HP. They can still hit people riding on the truck, pierce nonvital areas of the truck and come out the other side, etc.

Yeah, that works out to a reasonable result. But you're using a weapon with a relatively low rate of fire, which lets you get by in this scenario.

Can you propose an example where it does break?

[Langy]

Can you propose an example where it does break?

How about the same exact example, but with a minigun firing 30 or 60 rounds per second rather than the 8 rounds per second you were using?

Actually, the game does assume a point target. Shots at anything big enough to have "walls" are assumed to be at a 10-square-foot area; see p. B558. If you exceed the HP in that area, you cause a breach at that one point. For huge targets like buildings and aircraft carriers, the other hits simply don't contribute to the breach. They certainly still count as hits against the wrong target, which here can be crew on deck, protruding antennas, and anything else that isn't the primary 10-square-foot target. The rules don't say that if you fire a machine gun at a truck, all the bullets that "miss" magically bend around the truck; they just say that they don't contribute to chewing up the truck's HP. They can still hit people riding on the truck, pierce nonvital areas of the truck and come out the other side, etc.

I have to say I find this idea very silly, since you can't hit a 'nonvital' area of the truck even if you aim for one - all penetrating hits come off of HP, after all - apparently unless you make all of those hits really, really quickly.

Then again, GURPS already has problems with large things dying too easily to small things (for example, an autocannon sinking an aircraft carrier) due to the way HP scales with size.