Reverse Missiles / not an "attack"

[Rupert]

Originally Posted by Plane

makes me wonder what would happen if there was a pair of mages both w/ Reverse Missiles shooting at each other

That kind of dilemma could exist with a pair of 'Reflective DR' foes shooting at each other too.

Don't stand between them.

I'd rule the attacks would bounce back and forth until they ran out of range.

[Varyon]

Originally Posted by Plane

makes me wonder what would happen if there was a pair of mages both w/ Reverse Missiles shooting at each other

That kind of dilemma could exist with a pair of 'Reflective DR' foes shooting at each other too.

For the former, in the thread I linked previously, Kromm stated you should have the spells basically run a Quick Contest between them (using the skill level they were each cast at), and whichever lost winds up failing to protect - basically, the projectile bounces between them a few times until it manages to get past. If using this interpretation, for Reflective DR, you'd instead probably have the characters roll as though they were using Power Parries (to be clear, they aren't using such, we just use the same scores since we need something to roll against, and that seems the most appropriate option).

Personally, I think Rupert's option (they bounce back and forth until they run out of Range) is probably better.

[dcarson]

I'm now imagining two rows facing each other. When the missile gets to you and reverses you fire. Repeat. Then one row drops to the ground. Sort of a spell laser.

[RGTraynor]

Originally Posted by Rupert

I'd rule the attacks would bounce back and forth until they ran out of range.

With archery, a potential factor might be "how many seconds does it take for that arrow to do so?" For practical purposes, that's a detail GURPS avoids generally (at least as far as I've ever seen), but an arrow doesn't traverse a couple hundred yards in a second flat. Two? Three?

Originally Posted by David Johnston2

If it's a gun fight on both sides, then any dodging he'd do against bullets in general would apply to his reversed bullet. But what about firing from cover?

Seems like a GM would just have to apply common sense. If Shooter A is using a firing slit/pavise/sandbags, then the Reversed missile has the same penalties to hit him as any other ranged attack against Shooter A. If Shooter A is sticking his weapon over a parapet to fire blindly, then there's a chance (and not a great one) that the Reversed missile clips a hand. Etc.

[Varyon]

Originally Posted by RGTraynor

With archery, a potential factor might be "how many seconds does it take for that arrow to do so?" For practical purposes, that's a detail GURPS avoids generally (at least as far as I've ever seen), but an arrow doesn't traverse a couple hundred yards in a second flat. Two? Three?

A brief bit of Googling indicates a modern recurve bow tends to fling arrows at somewhere around 170 feet per second, while a modern compound bow tend to fling them at around 260 feet per second instead. Heavier arrows result in slower speeds, higher draw weight results in higher speeds, all else being equal. Part of me is tempted to try to work out a method of determining velocity - perhaps diving into "The Deadly Spring" - but I suspect that way lies madness. I'd say just go with Move 70 (somewhere between those two values) if it matters. Note there are rules for time of flight to matter in Tactical Shooting - they still resolve the hit instantly, but if it takes more than a second to arrive you roll 1d-4 for each full second, and add this to the character's effective skill (average -1.5 to hit per second, but it's possible for the foe to accidentally more-or-less walk into the path of the bullet, for a bonus), to represent that there may have been unpredictable movement or similar in the interim.

[Plane]

Originally Posted by Varyon

If using this interpretation, for Reflective DR, you'd instead probably have the characters roll as though they were using Power Parries (to be clear, they aren't using such, we just use the same scores since we need something to roll against, and that seems the most appropriate option).

It might be more interesting with variable DR (ie you buy 2d DR for the cost of 7 DR) or with ablative DR since the bouncing could get past a low roll or eventually wear it down.

[Varyon]

Originally Posted by Plane

It might be more interesting with variable DR (ie you buy 2d DR for the cost of 7 DR) or with ablative DR since the bouncing could get past a low roll or eventually wear it down.

Ignoring the bizarreness of variable DR (note that the Armor as Dice rules don't involve actually rolling for DR - rather, 2d DR reduces a 3d+1 attack into a 1d+1 attack), if using Kromm's suggested Quick Contest in a situation where the number of "bounces" matters, I'd give each character one free bounce (the effect normally doesn't have a chance of failure), then if they succeed at their roll, they'd get additional bounces equal to MoS+1 (once they run out of bounces, they get hit). So, let's say one character has MoS 3 and the other has MoS 5; the character with MoS 3 was the initial target of the attack (and thus has their DR apply first). These characters thus can have up to 5 bounces and 7 bounces, respectively, before the effect fails to work. So the first character has the projectile bounce off, then the second, then first, second, first, second, first, second, first, second... and finally the first character takes a hit and the sequence ends. But if the second character had Ablative DR, it's possible the first character could avoid that hit, if the second character's DR is depleted prior to bounce number 10.

Of course, as I stated above, my inclination would be more toward just having the projectile bounce between the two until it runs out of kinetic energy (or maybe just only let it bounce something like 2d-2 times total, after which it's too off-course and outright misses). In that case (particularly if not capping the number of bounces), particularly for characters who are close together relative to the range of the attack, you could have the projectile significantly deplete any sort of ablative/semi-ablative DR.

[Pursuivant]

Originally Posted by Varyon

Heavier arrows result in slower speeds, higher draw weight results in higher speeds, all else being equal. Part of me is tempted to try to work out a method of determining velocity - perhaps diving into "The Deadly Spring" - but I suspect that way lies madness.

An easy compromise which doesn't require lots of math would be to base missile speed on Bow ST with a multiplier for bow type.

For example:

Bow ST x 3 x bow type modifier = fps. FPS/3 = Move

Modifier

2 for Shortbows
3 for Longbows
+1 for Composite construction
+1 for Recurve/Compound construction.
+1 for TL7+ materials

E.g.,

TL8 ST 15 Composite Recurve Longbow = 15 x 3 x 6 = 270 fps = Move 90
TL 0 ST 10 Self Shortbow = 10 x 3 x 2 = 60 fps = Move 20.

[Anthony]

Originally Posted by Varyon

Part of me is tempted to try to work out a method of determining velocity - perhaps diving into "The Deadly Spring" - but I suspect that way lies madness.

Getting accurate answers pretty much requires computer modeling, but it should come fairly close to sqrt( 2 * energy / (arrow mass + M ) ), where M is a constant that varies with the shape and weight distribution of the bow.

[Pursuivant]

This thread is Part 8061 as to why GURPS 4E Magic needs a massive overhaul.

Reverse Missiles is an expensive spell with a big prerequisite tree, so it ought to be pretty lethal. Given all the possible situations where a mage might cast Reverse Missiles, it deserves way more than a single short paragraph explaining how it works.

My house rules/proposed fixes (collected from clever folks like you all, all the way from sometime in the last millennium) are in line with what other folks have proposed.

* If it flies through the air, it's not alive, is physical or magical, and has the ability to mess up the mage's day, it's an attack.

* Reverse missiles doesn't work against insubstantial non-magical attacks which don't depend on physical force. GM's discretion as to what counts as "physical force." Hostile gusts of wind count, psionic "mental stabs" which work at range don't.

* Missiles don't get any rebound energy when they're bounced back. If they're aimed at the mage from beyond 1/2D range, they don't make it back to the shooter. Likewise, spells/missiles which go past 1/2D range on the return, or otherwise weaken with range do less damage to the attacker when hit.

* Dropped attacks just randomly bounce away, landing at the same distance from the caster as the distance they fell.

* Shrapnel, etc. from ranged attacks which emerge at a distance from the attacker (e.g., grenades, artillery shells) just gets bounced back to the hex from which it originated.

* Anything between the caster, the attacker, and the reserved missile might get hit on a maximum roll of 9- on 3d.

* Roll randomly to determine which part of the attacker gets hit by a returning missile.

* The attacker gets all the benefits of Cover and Cover DR to defend against the returning missile. If the modifiers for Cover, Size, Range, Hit Location, etc. for the attacker to "hit himself" means the missile misses, it just lands in the attacker's hex. Cover DR protects normally.

* Attackers turned defenders get bonuses to Active Defenses against missiles they can see reversing and coming back at them. Usually +1, maybe +2 vs. slow and large missiles.

* Critical hits get through the shield and aren't reversed, but the attacker has to roll again to hit. Only a second CH means a true CH.

* For extra energy, the caster can block all missiles - even Critical Hits. If Critical Hits are reflected they automatically hits the attacker but roll against to see if it's a real CH.

This option makes Reverse Missiles even more brutal, but it's necessary if a mage hopes to survive massed missile or autofire. Otherwise, the law of averages will eventually turn the caster into a pin cushion/pinata.

* Cost can be pro-rated or the spell can be based on TL to defend against extremely heavy or powerful missiles. i.e., you might need to spend extra energy to defend vs. trebuchet shot or learn the TL6+ version of the spell if you want to reverse autofire bullets.

This gives needed game balance in campaigns where magic and high tech missile weapons coexist. While most GURPS Magic spells suffer at TL5+, Reverse Missiles gets turbocharged, making it an almost guaranteed fight ender vs. gun-equipped foes.

Reverse Missiles is NASTY against unsuspecting foes and completely screws missile-only fighters, especially high TL foes who aren't likely to have serious melee/unarmed combat skills.