Heirloom crossbow will not drop for me

At this point I wonder if I'm missing something or doing something wrong. I've been running Equilibrium since it came out. I have all 3 sets of armor. I have the legendary weapons. I have the black crystal. But the exotic just won't drop, even with the initial drop boosts. I just don't understand how I've run this dungeon 30+ times at this point and I just get the same things over and over