OGC:Volley (5e Variant Rule)
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The firearm is designed to fire multiple rounds at once. To keep things simple, treat the volley as a cone originating from the end of the barrel. Make a single attack roll against the target of the attack. After resolving that attack, all creatures within the cone (range equal to the weapons short range) must make a DC 12 Dexterity saving throw or take the listed damage. If the firearm has less than 5 barrels then the victims get advantage on their saves. This does mean that there’s a chance for the primary target to be shot twice!