Impromptu Ammunition is a trait in Destiny 2 that can appear on 31 weapons. An enhanced version exists on crafted and some newer weapons.
What Impromptu Ammunition does
Final blows increase ammo meter progress from all sources for a short time.
Enhanced version
Final blows increase ammo meter progress from all sources for a slightly increased duration.
Weapons that can roll Impromptu Ammunition (31)
AnarchyArc · Grenade Launcher
Bellowing GiantVoid · Rocket Launcher
Biting WindsKinetic · Combat Bow
Cataphract GL3Strand · Grenade Launcher
Coriolis ForceVoid · Fusion Rifle
Dawn Far OffSolar · Machine Gun
DEADHORSE 04Stasis · Submachine Gun
Dragoncult SickleStrand · Sword
Evening SI4Solar · Sidearm
FatebringerKinetic · Hand Cannon
Fatebringer (Timelost)Kinetic · Hand Cannon
Giver's BlessingKinetic · Auto Rifle
HammerheadVoid · Machine Gun
Hero of AgesArc · Sword
Kindled OrchidVoid · Hand Cannon
No FeelingsArc · Scout Rifle
Peculiar CharmKinetic · Submachine Gun
PermafrostStasis · Grenade Launcher
Reghusk's PledgeVoid · Auto Rifle
Returned MemorySolar · Sidearm
Sarpedon-DArc · Hand Cannon
Solemn RemembranceStasis · Hand Cannon
Stryker's Sure-HandVoid · Sword
SublimationArc · Scout Rifle
Subzero SalvoArc · Rocket Launcher
Sullen ClawVoid · Sword
Tatara GazeArc · Sniper Rifle
Tempered DynamoArc · Fusion Rifle
Temptation's HookArc · Sword
The Ringing NailSolar · Auto Rifle
The Spiteful FangStasis · Combat Bow