Detailed Shotgun Ammo – House Rule

I alluded to a set of house rules that I came up with for shotguns to deal with small shot sizes in my post on Rapid Fire rules and suppression fire.

I had thought I’d posted about them, but looking, I don’t think I did.

Here’s the deal: it’s commonly known that birdshot stinks as a person-killer. Granted, it’s probably better than harsh language, but not by much. The intimidation and suppression value will be large (see Cool Under Fire, Tactical Shooting, p. 34), and in the real world, that ain’t nuthin’.

Anyway, using my article and revised spreadsheet, it’s possible to turn the usual statistics about shotguns into a pretty detailed table.

A note about the previous version that you may have seen. The data was wrong. The lead pellets were too fast (and thus too-high in penetration, even more than they should have been) and the steel pellets were probably too many. I set the lead shot to 1275fps, mostly, except in a few cases where standard 2.75″ loads were different. The #1 Buckshot was only 1250fps; the 00 and 000 Buckshot were a heavy-kicking 1325. Steel shot tended to range from 1400-1550fps, so I settled on 1450, and 1 and 1/8 oz for steel shot, and 1.25 oz for lead, but I made whole-numbers of pellets. All in all, a lot of fiddling.

OK, that’s unreadable. click on the image (or here) to go to the full Excel file.

Point is, the calculated wound modifiers, the things in the squiggly brackets, drop below 0.5 (the value for pi-) pretty fast.

What I do is to cluster real pellets into “effective” pellets by ensuring every wound modifier rounds up to a full pi-. so everything smaller than #2 Lead Buckshot (1d+1 pi-) has an effective RoF lower than the number of pellets actually thrown. The clustering of pellets (and therefore damage and effective RoF, and therefore Rapid Fire bonus) means that there really are only a few different types of shot that are worth of GURPS’ resolution.

They are:

Every lead or steel example from 1d and lower has a more-or-less equivalent variant in the other material. So if you want to have a lead-free world, or steel shot hasn’t been invented yet, you can swap the materials for equal stats.

As shown in my musings about rapid fire, targeting, and using suppression fire to mimic scatter around a target, the relatively higher hit percentages using the corrected Effective RoF mean the number of pellets in a shot that actually strike home will go up to more sensible values.

Some notes on the table(s)

I tried to give a reasonable selection. A point change in damage was enough to get a row by itself, which explains down to 2 Buck. The rest, I collapsed all the identical rapid fire bonuses into one, but allowed differentiation by damage or, in one case, range. So #3 lead buckshot does 1d pi- but has a 1/2D of nearly 70 yds. Steel F shot also does 1d pi-, but the lighter pellets only have a 1/2 of 40 yards, but you get +1 to hit because there are more of them. So there’s a legit choice there.

+Hans-Christian Vortisch picked on my Max Range numbers, so I fiddled a bit. I set the program to calculate where the average penetration falls to a ludicrously low 0.017 points of damage. That put the actual max range for 00 Buckshot closer to his real-world number, and I just let the math roll from there.

The penetration/damage figure only takes into account projectile energy and cross-section. No mushrooming or funky stuff. It tends to get a bit wonky at low projectile cross-sections, because the low cross-sections force the penetration numbers up to an unrealistically high value. Regardless of what the KE/cross-section numbers look like, these low-mass, low sectional density projectiles won’t penetrate deeply. The wound channel modifiers (values in squirrely brackets) correct for that somewhat.

Still might produce unrealistically exaggerated penetration values, so another way to figure this is that zeros actually count as zero when rolling for damage. So if you roll a 1, 2, or 3 on 1d-3, you do no damage, not the usual “minumum 1 for pi.” This table has zero-penetration hits built into it. If you want to re-convert to the usual “minimum piercing roll is a 1,” then you map it this way:

1d	3.50
1d-1	2.67
1d-2	2.00
1d-3	1.50
1d-4	1.17
1d-5	1.00

So our 12G #9 Birdshot (1.07 points of damage) would be 1d-5 instead of 1d-3. The average damage on 1d-5 (minimum 1) is 1. The average on 1d-3 (minimum 0) is also 1. Either way can work; you probably will sort out different choices than those I picked above.

Parting Shot

This table started life as a super-detailed look at shotguns. It ended with what I think are better estimates of the effective RoF and damages of these loads for those who need them. The condensed table provides the right amount of choices (not stupid-high, but enough to differentiate) without useless detail.

Hope you enjoy!