Yesterday i tried the new Graves' with the new item Cull. I noticed that every bullet would apply the on hit lifesteal from cull. It didn't matter if it was against the same enemy.
However, hitting multiple bullets on the same enemy with a Black Cleaver only gave them one stack. I expected to apply 4+ stacks with a single auto as Cull triggered on every auto as well.
Now i am wondering if this goes for other on hit effects as well, such as Wits End. If graves crits and hits every bullet he would be able to deal 10 (with IE) x 42 = 420 extra magic damage(not calculating the resist shred).
I am also wondering how this interacts with Thornmail and Rammus. Would Graves take the thornmail + Rammus E damage on every shot? If it would work then graves would trigger this combination 10 times per basic. A Rammus taunting a Graves would pretty much always get a free kill.
Best Answer
This is speculation on my part, but I believe that Cull's on-hit heal is actually a modified lifesteal effect. Since the effect is determined based on the damage dealt and not on whether a hit landed, it makes sense that it would function normally with New Destiny. This would mean that each bullet triggers it.
Based on the above assertion how lifesteal works with Graves' passive, the damage dealt by Graves would incur the effect of Thornmail and Rammus W. My reasoning is that thorn effects are not on-hit class effects, they figure the damage dealt and return a percentage or flat amount of damage back.
Edit: This line from the LoL wiki (up-to-date on 11/19/2015) seems to support my assumptions:
Lifesteal and thorn effects are not one-use on-hit effects, so they apply for each pellet.