The key is to use the heavy attack button the moment you see your [Glaive] hit something.
Heavy explosions force a slash proc.
Normal explosions force an impact proc.
Although [Killing Blow] does not [Reflect] added damage to your explosion in the inventory, it bumped slash procs from 28k to 39k for headshot explosions.
Your bounce explosion is around 1.5 times your normal throw, while your charged explosion is around 2 times the damage of your normal explosion.
Using Volatile quick return turns your normal throw hit into -> 7.8 range,
1(normal) + 3(heavy) damage -> 1(normal) + 1.5(bounce) + 3(heavy) damage.
you can see it is a really good mod for net damage. Though the bounce damage wont scale into late game being blast with impact procs unlike the heavy explosion being blast with slash procs.
You can try [Condition Overload] for more damage, but it does not seem to proc for the first heavy explosion, giving me 28k slash procs when replacing [Killing Blow]. By the time you can do the 2nd explosion to take advantage of the forced procs, often than not, the heavy gunner is already dead. so it seems more comfortable just using [Killing Blow] for straight damage increase.
Overall, very nice to use in steel path. Even better with a riven