>>529206643
Okay so I just tested it.

Landed an impact directly on the front of the fleshmob.
Then shot it 22 times which killed it on the 22nd shot.

in total the breaker did 5445 damage to the flesh mob.
This means the impact did roughly 800 damage.
I took off 2 heads from the fleshmob, each roughly 400 HP.

If the explosion behaved normally,
I should be dealing about 300 damage to EACH body part which amounts to 3000 damage.
Even assuming I only hit the front half, I would be doing 1800 damage.

It's not conclusive, but it does definitely look like you only deal the explosive damage when the heads pop.