Maintenance for the week of April 20:
• [IN PROGRESS] NA megaservers for patch maintenance – April 20, 3:00AM EDT (7:00 UTC) - 12:00PM EDT (16:00 UTC)
• [IN PROGRESS] EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
Depends on the level of the target. Most veteran PvE are level 50. If you are V16 Major Breach reduces spell resistance by 5280. This gives a damage increase of 5280/50000 = 10.56% of the tooltip value. If against a V16 player then it will be 5280/66000 = 8% of tooltip value. Note that this value is decreased if you have any source of percentage penetration such as Nirnhoned or Sharpened.