Impact or time-fuse, you pick.
For an idea of the damage, fire a salvo at a wall from point blank.
They are hard to aim, but those who do get them to work advise firing a little high from 1-1.5K.
But that doesn't include speed and relative speed, I'd guess it's at nearly equal speed and no closure rate.
From my experience (in AH1 with B17s) if the formation is tight enough, 1 impact on the center plane can detonate the whole formation.
Usual result I'd get was touched plane'd explode and at least one other be barely flying.