GURPS Overhaul - Aiming

[Varyon]

This is an Aiming houserule I've recently worked out, and would like some input on. The first post is the high resolution version, the second is a faster streamlined version. The third post handles how to integrate this with my Initiative Overhaul.

I've essentially broken "shooting guys" down into a series of steps. The first is to observe the target and determine where you need to shoot to hit them. The second is to actually place your weapon into a position that will shoot the point you've chosen. The third is actually firing, which will impose some inaccuracy in the form of jittering, flinching, and so forth. At this point, the bullet has a point in space as its destination, but the weapon's inherent accuracy will knock it (slightly) off course. Random movement, windage, and so forth can throw it off course at this point - see Bullet Travel, TS32.


Observe Target: Determining the point to shoot is a Per-based skill roll. It is affected by target drift and optionally by bullet drop (see later). Retain your Margin of Success/Failure.


Weapon on Target: Putting the weapon into position is a DX-based skill roll. This is modified by the margin from above and the target's SM and Range (do not add Speed to this value, it's already accounted for). Bracing grants a +1 here. Again, retain the Margin.


Fire at Will: Pulling the trigger without spoiling your aim is another DX-based skill roll, modified by Margin from above, along with a further -4. On a failure, you simply miss outright. On a success, add MoS to your weapon's Acc/2 (round down, include bonuses from things like match grade ammo, shoulder stocks, etc) and assess speed/range penalties to determine if you actually hit.


Target Drift: Target drift is a function of bullet speed and the target's size, range, and relative lateral velocity, and represents how far the target will have moved by the time the bullet reaches them. For pistols against SM+0 targets with relative lateral velocity of 1 yard per second, this gives a +2 bonus up to 70 yards, and the bonus decreases by 1 every SSR thereafter (so +1 at 100 yards, +0 at 150 yards, -1 at 200 yards, and so forth). For rifles, it is instead +2 out to 150 yards and -1 every SSR thereafter. This assumes around 250 yards/second for pistols and 600 yards/second for rifles; for weapons with different velocities, divide velocity by 2 and round up to the nearest SSR to find where the weapon is at +0 to hit (so a 5,000 yard/second projectile is at +0 at 3,000 yards). For faster/slower targets, divide each range by relative lateral velocity in yards per second (against a Move 5 target, a rifle is at +2 at 30 yards). For larger/smaller targets, every +/-1 SM is +/-1 SSR to range (against an SM+5 target moving at Move 1, a pistol is at +2 at 500 yards). These two effects can be combined (against an SM+5 target moving at 5 yards per second, a pistol is at +2 at 100 yards).

Bullet Drop: Bullet drop is how far the bullet will fall off-target due to gravity before impact. The relationship is complicated (working out to something like -11 every 6 SSR until reaching terminal velocity, and -1 every SSR thereafter), but can be simplified as matching exactly to Target Drift, above, with relative lateral velocity in yards per second replaced by local gravity in G's.


Method of Attack: All of the above is for a standard Attack. A Move and Attack suffers from Bulk on the second roll and only benefits from Acc/4 (round down). A sighted shot (All Out Attack) grants a +1 to all three rolls. It also gives the player the option to abort before pulling the trigger, if he doesn't like his odds after the first two rolls.


Aiming: For Aiming, the character enjoys a +2 to each of the first two rolls, but must wait until at least the next round before he can actually fire. A second round of Aim gives a further +2 to total MoS, a third gives +1, and longer aiming uses the Precision Aiming guidelines (see TS26). When you do fire, you enjoy a +1 for All Out and benefit from full Acc. After Aiming, many shooters learn to pull the trigger slowly during exhalation to reduce spoilage - upon declaring that you will fire, roll 1d. On a 1 or 2, you fire this round. On a 3 or 4 you fire next round, and on a 5 or 6 you fire in two rounds (if the situation changes while you're waiting to fire, you can abort). Firing in this manner negates the blanket -4 when pulling the trigger. Optionally, you can fire faster with an in-between penalty - apply the penalty you actually take to the 1d roll to determine how long it takes for you to actually fire. If a character dislikes his rolls, he can abort and retry next round. A critical success on either of the initial rolls gives the option of using the margin as-is or rerolling it and being able to declare fire immediately (for example, if a character with effective skill 12 on the second roll rolls a 4, he can either accept a +8 to hit next round - possibly boosting it to +10 and +11 on subsequent rounds - or he can reroll and use the new margin immediately; if he opted to reroll and rolled a 10, that means he gets a +2 to hit and can actually fire now, rather than waiting until next round).

Aiming also opens the possibility of compensating for Range or Bullet Drop and Target Drift.

Compensating for Range: The above assumes the character has a good idea of the range to the target (that is, he knows the range band the target falls in). If he doesn't for some reason, don't factor in the target's range, drift, and SM when determining if he will abort during a sighted shot (that is, the player rolls without these modifiers, then they are added back in once he opts to actually fire). If, on the other hand, he knows his target's actual Range (see Rangefinding, TS27), and you aren't using Bullet Drop, reduce the penalties for Range. This negates -3 for knowing exact range, -1 for knowing range within 1 yard.

Compensating for Drift and Drop: If you have at least a decent idea of the range to the target (from which you can intuitively determine speed), you can compensate for target drift when firing. Rather than using the actual range to the target, use how close you are to knowing the actual range. Knowing Range within 15 yards for a pistol or 30 yards for a rifle (bullet velocity/20, round up to nearest SSR) is good for a +2 to hit; every +1 SSR to range is -1 to hit. As usual, divide range by the target's relative lateral velocity in yards per second. Again, note this bonus/penalty replaces the default drift bonus/penalty!
Compensating for Bullet Drop is the same, except you divide range by local gravity in G's. Note that if you adjust for Bullet Drop, Compensating for Range is no longer an option - the two rules are meant to be different versions of each other (Bullet drop is more lenient but gives less of a bonus than Rangefinding; the GM should decide which is going to be used in the campaign; an Extra Option Perk may justify being able to use the other).


Gunslinger: This new system changes things a bit for characters with Gunslinger.
Acc: If you wish to maintain the advantage of pistol-wielders over riflemen found in Basic Set, replace Acc/4 (Move and Attack) with Acc/2, and Acc/2 (Attack without Aiming) with Acc.
Drift and Drop: Gunslingers intuitively know where to put the bullet to compensate for these issues. Unless making a Move and Attack, they enjoy a +2 for negligible Target Drift and a +2 for negligible Bullet Drop (if using those rules).
Steady Pull: Gunslingers pull their triggers perfectly every time. They do not suffer a -4 for a too-quick trigger pull.
Stunts: All the various normal benefits of canceling/reducing penalties and serving as an Unusual Background still apply.


Dodging: Optionally, avoiding getting hit by bullets and the like involves dodging the shooter's aim, but a shooter can attempt to adjust for such evasive movements. For sighted shooting, when the shooter finishes the second step have the target declare intent to Dodge. The shooter may opt to take a penalty for Prediction Shooting. The target then rolls Dodge normally. On a success, the target subtracts 3*MoS from the shooter's MoS (MoS 0 subtracts 1). On a critical failure, the target dodges into the shooter's aim, giving the shooter +3 to the following shot. At this point, the shooter may opt to fire or abort.

Aiming is slightly different. When the shooter takes an Aim maneuver, a successful Dodge only subtracts MoS from the shooter's MoS (MoS 0 subtracts 1). The target may attempt to Dodge every round of Aim and the round upon which the target fires; each attempt subtracts from MoS and can stack. A critical failure here means the shooter may opt to fire immediately or get a +3 to the eventual shot.

If the shooter is taking his time to avoid spoilage of aim, treat this as extra seconds of Aim (although note that the shooter gets no further benefit from this).