Now I could be wrong about this, but i never really see this interaction and don't have a method of testing it at the moment.
If grave's auto applies multiple stacks of 
( 1 per pellet that hits i assume)
Then shouldn't he be able to instantly activate 
passive on a target? Due to the same mechanic of individual projectiles being considered different damage sources.
Annoxis2 votesBlack Cleaver Shredding armor effect is a on-physical damage effect. Since each pellet of Graves deal his damage independantly, they each count as a different instance of physical damage.
To proc the passive of Braum, you don't need multiple instance of a special kind of damage, you need four instance of on-hit effect. Graves' AA count as only one instance of on-hit effect, therefore, Graves need four AA to procs it.
deadlychuck1 votesMake sense if they pass on-hit effect to the target object.
Annoxis1 votesI have trouble understanding what you are saying here...
deadlychuck1 votesSorry, i'm speaking from a coding prospective.
It's hard to explain object and class types, but basically, when one thing in the game, champion, minion, tower, monster, abilities in some cases, does something to another champion, minion, exc.
Riot controls what information is being passed and received between the two in the "interaction". This is probably why their death ~~crap ~~ cap (lul i actually typed crap by accident) system is the way it is, because they were inconsistent in what kind of data were able to receive or sent from different types of objects.
In fact, this is probably how they define an ability to be a "projectile" when it comes to things like yasuo windwall or braum wall. If the data is coming from a champion object, then it's not blocked, but if it's coming from an independent ability object, then the ability is deleted or w/e. They probably class things like AOE spells differently.
Slythion1 votesThe difference is that Cleaver is proc'd off damage sources (so each individual pellet of an auto from Graves) while Braum's is proc'd by auto attack sources, not just generic ad source.
So even though his auto produces multiple projectiles, I'd assume each of those pellets are coded to be part of the same "auto" from graves while also being coded to be independent sources of damage, and so that's why Cleaver passive is produced by each pellet while Braum passive is proc'd only from the generic "auto"
deadlychuck1 votesExcept riot has admitted somewhere before that they can't track independent instances of damage. It's probably something to due with how the class objects are set up, but basically from what i can tell, the damage source isn't passed to the objects being hit.
Which is why you have cases of things like thunderlords activating on the 3rd tick of morg pool.
Slythion1 votesthat's another possibility, depending how long ago they talked about tracking independent instances of damage, it's possible that they are able to now when they rebuilt the code around the time of the new client.
shrugs it'll all guesswork though
Darkdemon6531 votesExcept riot has admitted somewhere before that they can't track independent instances of damage. It's probably something to due with how the class objects are set up, but basically from what i can tell, the damage source isn't passed to the objects being hit.
Which is why you have cases of things like thunderlords activating on the 3rd tick of morg pool.
http://leagueoflegends.wikia.com/wiki/Adaptive_Helm
Morgana's W can proc TD on its own because TD procs when a champion is hit with an ability three times, not when a champion is hit with three abilities.