A 12 gauge shotgun shell. This ammo can come in many forms:

Ammo TypeScatterSpreadEffectsBest Against
BuckshotScatterSpread X 50Groups at close range
Slug+50% damage, Piercing 3, Medium RangeArmored single targets
Incendiary ShotScatterSpread X 25Burn X 2Unarmored groups, area denial
FlechetteScatterSpread X 25Bleed X 2Lightly armored groups
Bean BagNon-lethal, Knockback 1, FatigueCrowd control
Dragon’s BreathBurn X 3, Cone AttackHallways, chokepoints