Shotguns are an interesting beast in any game, and GURPS is no exception. A while back – Jan 2014 – I posted some alternate stats for shotguns, using my ballistics program. Some recent questions on that particular post – over a year ago, plus the fact that actually shooting shot from a shotgun, as opposed to slugs, plays into recent questions on multi-projectile rapid fire.
First, what’s going on with my rescaling?
The figures of interest for shotshell include the number of physical pellets in a shell, and the energy of each pellet. The calculations follow the usual pattern – but you run into scaling issues as the pellet size drops.
Down below 4mm or so, the scaling of the penetration with pellet diameter may produce non-physical results. The pellet diameter gets pretty small for some of these.
In any case, the issue that you run into is that the rules as written provide for dozens to hundreds of pellets with relatively poor penetration and damage capabilities. The way that I deal with the wounding is that the small pellets have a terrible wound channel modifier – much less than even a pi- (0.5 WCM) would give you.
The trick that I use is to collect pellets into groups – each of which brings the wound multiplier up to a “full” 0.5. So if, for example, Steel #2 shot has 141 pellets, but each one only will do a wound that would scale as a 0.15 instead of 0.5 for wound channel. So I collect the pellets into groups of 3.33 pellets each, bringing the RoF from 141 down to 42.
Now, collecting the pellets like this doesn’t change the penetration score – though perhaps it should. The penetration ranks at about 2.23 points.
Now, for very small pellets, there really should be an exemption to the rule that any piercing weapon does at least 1 pt of damage. So I’ll make one. This changes the math a bit in terms of mapping damage to dice:
1d: 3.5 pts
1d-1: 2.5 points
1d-2: 1.67 points
1d-3: 1.00 points
1d-4: 0.5 points
1d-5: 0.17 points
In this case, it doesn’t quite make the cut for 1d-1, but instead ranks at 1d-2, but if you roll a 1 or a 2, you don’t do any damage.
That makes 1d-2 pi-, but with “only” 42 shots. Still, each pellet should have somewhat reduced ability to penetrate armor, if not flesh. Adding an armor divisor equal to the ratio of the collection factor for wound channel might work, but would require playtesting.
This brings the example steel #2 shot to 1d-2 (1/3) pi- with RoF 42. That’s a +4 bonus to hit instead of the usual +6.
No funky rules – if you hit, you roll 1d-2(1/3). The max penetration you can roll is 4, which means that DR 2 is completely proof against this small shot. On a hit on unarmored target, injury will be 0 to 4 penetration, halved. So maximum of 2 points per hit, but if you have DR 1, you will still take 1 point per hit.
Using the table that I created in the previous post, and the new rules, smallshot is only dangerous at close range and against unarmored targets – more or less just as it should be. The collection of wound channel mods into groups helps tame (a bit) the RoF issue where the smallest shot (#9 lead shot) has over 700 pellets in it. +9 bonus more or less, I think. But with the downscale in wounding, 730 turns into 73, which is still +6. With 1.07 penetration per hit, that’s about 1d-3 as well
That puts #9 lead shot – a pellet 2mm in diameter, compared to 8.4mm for 00 buckshot – at about1d-3(0.1) pi -, with a +6 bonus to hit due to number of pellets. Even DR 1 will repel the shot completely (and truthfully, even DR 0.3 is enough), which again means that unless you’re in “boom-stick” range (half of 1/2D? quarter of 1/2D?) which is something like 5-10 yards, you’re probably safe.
Again, as it should be.