Sacrosanct
Legend
Curious, for those who know more about firearms, how would you represent the special ammunition that are available for shotguns? Such as the dragon breath rounds.
I can imagine sneaky goblins using illusion to appear as dragonborn, firing dragon breath from shotguns at a group of humans. They leave one or two survivors who tell the tale of being attacked by dragonborn. If a war starts they then clean up after both sides expend themselves.
Most gimmick rounds wouldn't have much of a significant difference in gameplay to warrant changes. Like flechette rounds. For dragonsbreath, most of the initial damage is still from the magnesium pellets hitting you, so the only change I would make is to give it an incendiary ability (sets flammable targets on fire, maybe 1d4 points initial damage and 1d4 at the start of your next turn if not extinguished).
It all depends on how detailed you want. But beware the rabbit hole I mentioned earlier. Most shotgun rounds, in a modern setting, would be:
birdshot: damage only out to 10m, any armor offers total protection, double prof bonus to hit
buckshot: standard damage and range (I would list it at 25m), double prof bonus to hit
slug: 100m range, standard prof bonus to hit
bolo: same as buckshot
dragonsbreath: same as birdshot for pellet damage, fire damage out to 30m (if you want to get super realistic, every subsequent round has a 25% cumulative change of jamming because it fouls the barrel so much)
FRAG-12 grenade: 1/4 damage and radius as 40mm grendade
flash thunder: no damage, but acts like stun grenade (flash/bang)
armor piercing: ignores armor bonus, standard prof to hit, 100m range, half damage
flare: like a flare gun, no damage
gas: half the radius of a gas grenade (like tear gas), no damage
bean bag: stun damage only
screacher: no damage, just a loud screeching noise (used to scare animals)
Anything other than buckshot or birdshot or slug I'd have a lot higher cost of ammunition as well.