Handling Long-Range Musketry

[Varyon]

This is a spin-off from the What kinds of firearms would people start making [After the End]? thread, wherein there was some debate over how accurate smoothbore muzzleloaders should be, with a nod toward their strange exterior ballistics (namely, that they have a bad habit of deviating from their aimpoint more rapidly than standard GURPS Range rules suggest - this is due to a combination of factors, from not being a perfectly-smooth sphere to changes in trajectory due to spin).

Based on the numbers from a Master's thesis linked in that thread, I think I have an idea of how to handle this in GURPS. In that, at some point between 50 yards (-8 to hit) and 80 yards (-10 to hit), the projectiles picked up somewhere between -3 and +2 to skill, with an average of -0.111 (I approximated this using 1d-4). Beyond this, there was something like a further -1 to hit at each -1 from Range, for a total of -2 per point of Range. The shots only went out to about 170 yards, however.

Still, from this, a bit of a pattern emerges. A low resolution solution is to double all Range penalties beyond 70 yards, so that a musket sees range penalties as (...-7, -8, -9, -11, -13, -15, -17...). A bit higher resolution option would be to replace the first -1 with 1d-4, and you could possibly push the range back a step, with (1d/2)-2 beyond 50 yards, rounding normally (so you'd be between -1 and +1 to hit). A much higher resolution option would be to do something like (1d/2)-2, 1d-4, 1d-5, 1d-6, 2d-10, 2d-11, 2d-12, 3d-16, and so forth (although I'd replace each nd with 1dxn, so that you don't get a tighter spread with each added die).

The range at which this starts to come into play is going to vary. The above is perhaps appropriate for an Acc 2 weapon (not certain how good the weapon used in the testing was). Each +1 to Acc from being Fine (Accurate), opting for Careful Loading, and so forth, is +1 SSR to the range beyond which the above effect comes into play. Higher-quality ammunition may also be available - while typically below GURPS resolution, such ammunition is double cost but is +2 SSR to the above range (and this does stack with Accuracy modifiers). Each -1 to Acc from being Cheap, black powder fouling, and so forth, is -1 SSR to the above range. Using field-expedient projectiles drops the range due to Acc penalties and gives a further -2 SSR to the range.

Do keep in mind that, with the sorts of penalties the character is already going to be suffering for Range (by default, the above rules kick in at 100 yards, or 70 if using (1d/2)-2, which correspond to penalties of -10 and -9, respectively; a base Acc 1 pistol firing field-expedient projectiles is about the worst situation possible, and even it doesn't see an effect until it's at -7 or -6 from Range), the above typically isn't going to make much difference, and can probably be safely ignored in most campaigns. If a musketeer sniper harms your Sense of Disbelief, however, the above is a way to handle that. If using Tactical Shooting, note that the above modifiers come into play after the MoA-based skill cap.