Darktide - Long Bomb Achievement

Warhammer 40k:Darktide Veteran Sharpshooter has an achievement to kill 3+ enemies with a frag grenade airburst basically. You can't let the grenade bounce or touch anything, but it has a pretty long explosion delay. It's a pretty annoying challenge. There's a lot of areas with some reasonable distance, but often there's a ceiling blocking the way or some other issue. After flinging grenades all around the maps, this was the best spot I found for it. There's a long, open walkway that's always full of enemies. The reward is some torso/body armor.