History of Reverberation

Reverberation is a basic Trait weapon perk, listed by the wiki as introduced in Season 24. Final blows with the weapon increase the size of its detonations for a short duration. It is a utility perk for explosive weapons. It is most often seen on Grenade Launchers, where a bigger blast makes groups easier to clear, and it also rolls on the Sidearm Unfall.

Numbers

The sources checked do not give the size increase or the exact duration. Both describe the duration only as short.