For above poster, the 6 yard spread is for the random raid damage 'cannon' that the Juggernaut has. It deals high splash damage so stacking together just forces unnecessary damage upon the group.
We killed this boss for the first time on Wednesday, it took us about 15 attempts, but during that time we ironed out a lot of these 'RNG' deaths and came up with a strong rotation to handle the fight. With the phases being on a 3 minute 'conveyor', it lines up nicely with the vast majority of raid cooldowns.
Here's some things to remember:
1. Any raid member who can handle a mine confidently should try to deal with the one farthest away from the other two. We used our warlock with a Hand of Protection on the first set and Cocoon on the third set. As a warrior tank, I was able to handle all 3 mines due to high mobility, but our paladin struggled to do the same.
2. RNG seemed to kill off our raid members a lot. To cut this down we put ranged dps at max range from the boss, 9 times out of 10 this will stop the borer drills hitting them. We also spread the ranged out a lot in this phase to reduce barrage damage assuming the group couldn't move quickly enough. We told everyone that moving was by far the most important part as the Berserk timer really isn't that tight, as definitely wont be with gear like yours assuming your dps play properly.
3. For phase 2 we had a marker dropped close to the boss and another at the back of the room towards where Galakras is fought. We let the first Shock Pulse knock us back there as per the usual tactic. We tightly controlled this phase to reduce incoming damage as much as possible. We had a set up with a lot of raid cooldowns, which is something you seem to lack a little. Here's what I would do for your group;
At the beginning of phase 2, stack loosely around the marker and let the tar drop down. Then everyone moves ONTO the marker close to the boss.
1st Shock Pulse
-Power Word: Barrier - this may seem like a waste but the initial knockback damage is the only real thing you're able to mitigate. This is because when you reach the back of the room, you NEED to be spreading out to reduce incoming damage from the splash cannon.
-When you reach the back have 1 shaman drop a healing tide. SPREAD your raid group out 6yds and kite the laser forward using healthstones and personal cooldowns.
2nd Shock Pulse
-Quickly stack upon the marker and drop another Barrier.
-Spread out and drop second healing tide.
3rd Shock Pulse
-Stack and Spirit Shell/Healing Tide (assuming you have your third shaman).
-Spread and use a hymn.
Ensure during this time that both tanks are taking mines, along with anyone with a reliable immunity. After the third pulse, have your less mobile tank pick up the boss and let your other tank soak up any mines remaining.
4. Have your 2nd tank taunt at 2 stacks, and then subsequently at 3. This will align you with the mine timers.
5. Spam heal people with laser burn and implore that people use personals if they take too much damage.
6. If you can, have your raiders dodge ricochet as best they can. The most important thing, of course, is to have the group SPREAD during phase 1 to avoid it hitting multiple targets.
I really hope this gives you some information that you haven't already tried. If your raiders are taking too much damage from Borer Drills or Richochet they will die so it's down to you to ensure they realise the importance of avoiding damage wherever possible.
Best of luck,