Couple Notes on the Marks T18 2pc Set Bonus

In one of the PTR builds released last week, Blizzard fixed an issue where the MM 2 piece set bonus (4 seconds of Rapid Fire) was not applying Careful Aim.  Now that it is correctly increasing the Crit chance of Aimed Shots, someone in the SimC IRC asked what happened if the 2pc Rapid Fire happened at the same time as our normal Rapid Fire (wondering if the Haste effect stacked).  After looking through dozens and dozens of MM logs from Hellfire Citadel, I was unable to find any examples of the two buffs occurring at the same time, but I did finally find an example (twice in one fight, oddly enough) of one of the buffs cutting off the the other.  After searching through more logs, I (and Jademcian and Lokrick, who do the real work on SimC) feel fairly confident that this is how the 2pc Rapid Fire works: when you cast or proc Rapid Fire while Rapid Fire is already active, whichever has the longer duration will replace the other.

That is to say, if you have, for example, proc'ed the 2pc Rapid Fire at second 0, then at second 2 you cast your normal Rapid Fire, your normal Rapid Fire will cancel out the 2pc proc, and you'll have a fresh 15 seconds of Rapid Fire.  If, on the other hand, you've already cast Rapid Fire, on what we'll again call second 0, and on second 12 you cast a Chim Shot which proc's the 2pc Rapid Fire, it will cancel out your normal RF and give you 4 new seconds of Rapid Fire (because, 4 seconds of the 2pc RF is longer than the 3 seconds you'd had left of the normal RF).  And finally, if you cast your normal Rapid Fire at second 0, and then cast a Chim Shot which proc's the 2pc Rapid Fire at second 8, nothing will happen, because the 7 seconds of normal RF left is longer than the 4 seconds of 2pc RF would be.

Taking Advantage of the 2 Piece

Now that the 2pc set bonus is applying Careful Aim, we'll have to make sure we're taking advantage of that extra crit as much as possible.  As has already been mentioned on this blog, to do this we'll have to pay a bit closer attention to our focus pooling.  We want to be at nearly full focus when Chim Shot comes off CD, just in case we proc Rapid Fire, that way we can quickly spam out several Aimed Shots crits.

The other thing to pay attention to is when the 2 piece is proc'ing and your normal Rapid Fire is about to come off CD. In the graph shown above, this hunter cast Rapid Fire while his 2 pc Rapid Fire was already Proc'ed, thus costing him about 3 seconds of Rapid Fire.  Unless you're just very good at always looking at your buffs icons, this means you'll definitely want a Weak Aura or Tellmewhen icon set up to let you know when the 2 piece has proc'ed.

Of course, if the 2 piece proc's when you've already cast your normal Rapid Fire, there's not much you can do about it. As by far your most damaging shot, you do not want to delay Chim Shot for the 15 seconds of Rapid Fire.  There are times when Chim Shot comes off CD during the last few seconds of Rapid Fire; so I thought it might be worth looking into whether or not it's worth it to delay Chim Shot for a few seconds, just in case you proc'ed the 2 piece, which I'll get to in just a moment. First we need to understand a bit more about the 2 piece proc's during Rapid Fire.

2 Piece Proc's During Rapid Fire

As I've mentioned before, we're not going to see a lot of proc's from the 2 piece set bonus. Let's say, for example, you're a heroic raider in pretty good gear with a 37.5% Crit chance. That means you have a 15% chance to proc the 2 piece every time you cast Chim Shot (0.375*0.4=0.15).  That means you're looking at getting roughly 1 proc every 60 seconds (9/0.15=60, and yes, I used 37.5% crit so that it would be 1 proc per minute).  

Since Chim Shot has a 9 second CD, if you use both Chim Shot and Rapid Fire on CD, you'll end up casting about 1.667 Chim Shots during Rapid Fire (on average, of course).   That means your chance to proc a 2pc Rapid Fire during your normal Rapid Fire is about 23.73% (that is: 1-(1-0.15)^1.667 = 0.23732).  

A more useful way to think about that, perhaps, is that you're going to get about 12.5% of your 2 piece Rapid Fires during your normal Rapid Fire.  So instead of the 6.667% up-time we'd get if we didn't cast any normal rapid fires (4sec/60sec), we can only expect to see about 5.833% up-time in this example.

Delaying Chim Shot during Rapid Fire

Back to our original question "is it worth delaying Chim Shot for the last few seconds of Rapid Fire?" We only need a bit more information.  In 700 ilvl gear on the PTR, my AiS hits average 31766.6 damage, with crits averaging 78818.8 damage.  My Chim Shot, averages (hits and crits together) 106976.7 damage.  If we only look at the extra damage from Careful Aim (there's also some extra damage from haste, but it's negligible enough that we'll ignore it for now), 4 seconds of Rapid Fire, if we could manage to get lucky with TotH proc's, and spammed 4 Aimed Shots, we'd get an extra 188,208.8 damage (compared to using those same GCDs for Aimed Shots without Careful Aim).  However, we'll only get that extra damage 15% of the time (since we have a 15% chance to proc the 2pc Rapid Fire, as noted above).  That means our expected value for delaying Chim Shot 4 seconds is only 28,231.3.  

Since if you delay Chim Shot for 9 seconds you've lost the entire damage of one Chim Shot, it's fair to say delaying it 4 seconds will on average cost you four nineths of a Chim Shot, which is 47545.2 damage.  We can run a similar comparison if we only had to delay it any number of seconds, which will look like this:

	Gained from 2pc RF	Lost delaying Chim Shot
1 sec	7057.83	11886.3
2 sec	14115.66	23772.6
3 sec	21173.49	35658.9
4 sec	28231.32	47545.2

In all of these situations, we'll, on average, lose more by delaying Chim Shot than we'll gain by getting extra up-time on Rapid Fire.  

TL;DR

1. Pool up focus before every Chim Shot so you can spam Aimed Shots if the 2pc Rapid Fire proc's.
2. If the 2pc Rapid Fire has proc'ed, do not cast your normal Rapid Fire until the 2pc finishes. 
3. If you've already cast your normal Rapid Fire, continue using Chim Shot on CD as you normally would, as it does too much damage to ever ignore/delay.