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Old 05-13-2016, 10:58 AM   #1
Join Date: Jun 2013
Default Redefining GURPS Acc

A tangent in my Handling Long-Range Musketry thread talked about the possibility of modifying the various GURPS Acc rules. Below is a suggestion of what could be done - I'd very much appreciate input on this suggestion (both comments on it and possible numbers to use), as well as alternate takes.

First and foremost, this suggestion is intended to be used alongside Douglas Cole's On Target (Pyramid #3/77) article. A lot of my suggestions below won't make sense without that article, so consider it Required Reading.

GURPS Acc is a combination of the weapon's inherent precision, the quality of its sights, the ergonomics of its design, and a myriad of other factors. The intent here is to split this up to give us better resolution.

First off, we'll have a new stat, Ergonomics (Erg). This represents how easy the weapon is to get - and keep - on target. Erg applies to the Aim roll. First off, a longer barrel is easier to properly aim. Barrels are defined as VS (compact pistol), S (pistol, short SMG), M (SMG, short carbine), L (carbine/rifle), or VL (sniper rifle). VS has a default Erg of -2, S is -1, M is +0, L is +1, VL is +2. Sights modify Erg. Lacking any sort of sights means the shooter must sight along the barrel, which gives a -2 to Erg. Improvised sights, damaged sights, or severely misaligned sights are at -1 to Erg. Properly zeroed iron sights are the assumed default, for +0 to Erg. Improved Visibility Sights eliminate up to -3 in darkness penalties to Aim. Collimating and Reflex sights, as well as Targeting Lasers and Targeting Lights, are incredibly useful for Aiming - in addition to the +1 to Guns, such sights eliminate all darkness penalties to Aim and grant a +2 to Erg (for a net +3 to Aim). Using Telescopic Sights actually makes sighting on the target more difficult - they give a -2 to Erg per +1 to Acc of their current magnification level. If this penalty makes the difference between a successful Aim and a failed one, halve it for the next Aim attempt (if using Variable Aim or similar, a successful Aim eliminates the Telescopic Sight penalty for subsequent Aim attempts). This replaces the normal rule for Telescopic Sights penalizing Aim in the article.

Next up is Accuracy (Acc). This is how much of a bonus you get for successfully Aiming. As with Erg, barrel length plays an important role - although in this case, it's because a longer barrel both makes for a more precise bullet trajectory and a more accurate sight picture. VS has a default Acc of +0, S is +1, M is +2, L is +3, and VS is +4. Using a shoulder stock gives a +1 to Acc. This assumes a modern rifled barrel. Smoothbores are at -1 Acc, and firearms from before TL6 suffer a penalty equal to (TL-6). Using match-grade ammunition (or Careful Loading for multi-part ammunition) gives its normal bonus to Acc. Having an attached socket bayonet reduces Acc by 1. All of these modifiers add to base Acc, which is important for determining later effects. Telescopic Sights give their normal bonus to Acc, and cannot improve Acc to a higher level than all the previous effects combined (that is, a weapon that would be +4 for a long barrel and shoulder stock cannot benefit from more than a +4 to Acc from a 16x scope). Damaged, missing, mis-aligned, and improvised sights all give the same penalty - -1 Acc - and better sights simply make the weapon easier to Aim (via improving Erg). Regardless of Acc, the bonus from Aiming can only serve to negate Range penalties. Sights, targeting aids, and so forth do not modify base Acc.

A weapon's Precision (MoA) is a measure of how close to its nominal aimpoint the bullets tend to actually hit. MoA is a cap to skill - before factoring in modifiers for Range and SM, a character's effective skill cannot exceed MoA. If you know the weapon's real-world Minute of Arc, you can determine GURPS MoA in the following manner. Divide Minute of Arc by 36, read this value as yards on the SSR table, and find the Range bonus/penalty that matches this. Add this number to 20 to determine your skill cap. This assumes the Minute of Arc value you found was for somewhere around 74% (apparently, most are for something like a 69%, which is close enough) - if it wasn't, find the skill level that it was closest to, subtract 12 from this, and add the result to the number you calculated above. If you do not know a weapon's real-world Minute of Arc, a decent approximation is, as described in Tactical Shooting, to multiply base Acc (RAW or as calculated above) by 2 and add this to 22. Low TL firearms typically have much lower MoA than implied by their Acc, however - a musket (RL MoA 36) has around MoA 22, while a rifled musket (RL MoA 18 or better) has around MoA 24. Modifiers that add to or subtract from base Acc give a +2 to MoA per +1 to Acc.

Our final number to look at is Bulk. This is determined and functions normally, but also applies to a lesser extent at range. Penalties from Bulk, when applicable, apply to both Aim (where they are halved) and Attack actions. Weapons suffer their normal Bulk as a penalty when in Close Combat or using Move and Attack. At 1 yard, the penalty is instead Bulk+1 (maximum 0). At 2 yards and beyond, the weapon suffers from the worse of Bulk+2 and Range. Telegraphic Attacks (if close enough to make them), in addition to the normal effects (+4 to hit, +2 to enemy defense), also negate up to -2 to Bulk. Acc from successfully Aiming can negate penalties from Bulk, if you are close enough that these exceed those from Range.
If you desire further complexity, fast-moving foes can cause a weapon to suffer more from Bulk (as it's difficult to move the weapon around to keep tracking the target). If the target is within the range where Bulk+2 is worse than or equal to Range, each -1 to hit from the target's Speed+Range (as opposed to Range alone) becomes a -2. If the target is outside of the range where Bulk+2 is worse than or equal to Range, find how many steps (-1's) your current Range is from the Range set by Bulk, and add this to the difference between Speed+Range and Range. If the result is 0 or greater, simply use the normal Speed+Range penalty; if the result is less than 0, add it to the Speed+Range penalty. In either case, the character's total penalty cannot exceed Bulk + Speed+Range.

In addition to the above, there are some further considerations. First off, Fine (Accurate) and Very Fine (Accurate) actually serve to improve both Erg and base Acc (and thus MoA), while Cheap reduces both Erg and base Acc. You can also improve Erg by personalizing your weapon - getting the sights and length of the stock just right for you, getting just the right grip, and so forth. This is probably something like +0.25 CF (or perhaps a flat price), gives +1 to Erg, and makes the weapon eligible for a Weapon Bond.

Another consideration is for sights. Sights and targeting lights/lasers are typically zeroed to a specific range (for example, 85 yards). Round up to the nearest Range on the SSR table (100 yards for our example), and divide by 10 (round normally; this is 10 yards for our example). Any target within this range of the actual zero (from 75 to 95 yards) is targeted at +1 to Aim and +1 to Sighted Shooting. Any target within half this range (5 yards, so from 80 to 90 yards) gets a further +1 to Sighted Shooting (total +2), and any target at exactly this range (85 yards) gets another +1 to Sighted Shooting (total +3). This replaces the bonus for knowing the target's exact range - you need to actually adjust your sights to get the bonus if it doesn't match your current zero. Some weapons have multiple sights at different zeroes. A weapon can have two such without much difficulty, but with more than that you must make a IQ-based Guns check at -3 (and further -1 per sight beyond the first two) to remember which sight corresponds to which Range and match it to your current target. Failing this check means you're at -2 to Aim and -1 to Sighted Shooting.

Bracing also needs some discussion. Weapons with shoulder stocks can be partially Braced - this is in fact the default for Aiming with such weapons, and gives a +1 to Erg. Bracing via using both hands (for pistols), a rifle sling (for longarms), or similar portable method gives a +1 to both Erg and Acc. Bracing using the environment or an attached bipod or similar restricts mobility, however, for a -1 to Erg and +1 to Acc. These options do not stack with the +1 to Erg for partial bracing.

As a final note, it may be possible for low TL weapons to overcome their innate Acc and Malf. penalties. This requires using specially-made ammunition - perfectly smooth, polished bullets and higher grades of powder. For TL 5 and lower, +1 to Acc and Malf. consistent with 1 TL higher is 5x the price per shot (typically, this means it goes from $1 to $5). For TL 4 and lower, +2 to Acc and Malf. consistent with 2 TL's higher is 20x the price per shot ($1 to $20). The Acc bonus only applies to the specific weapon the ammunition was designed for (much like hand-loaded match-grade). The +1 Acc option cannot increase Acc by more than 50%; the +2 option cannot increase it by more than 100%. Cheap weapons get no benefit from using such ammunition. Fine (Accurate) weapons always get the Acc benefit, Fine (Reliable) always get the Malf. benefit. Good quality weapons (or those that are Fine in only one way) get half the benefit (round down) unless such ammunition is used in conjunction with Careful Loading. Optionally, an intermediate level of Fine is available, which is +0.5 CF and allows the weapon to benefit from such ammunition without issue.
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aiming, firearms, weapon design

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