Swashbuckler

Swashbuckler is a weapon trait: "This weapon gains increased damage from melee kills and kills with this weapon." Weapon kills grant one stack for 4.5 seconds (up to five, refreshing on gain), while a melee kill instantly grants all five. Reported bonus per stack is 6% (6/12/18/24/30% at one to five stacks) in one reference and 6.7% (up to 33.3%) in another, so the exact numbers may depend on the game version.

It is notable on Heavy ammo weapons such as the Grenade Launcher Interference VI, the first grenade launcher able to roll it with Clown Cartridge. Compare Rampage, which needs several kills.