I did the DFA strikes 80+ times before it finally dropped. I did the Zokris strike 25+ times before the Braytech RL dropped I got Duty Bound on about the third or fourth attempt and a second Duty Bound the very next try. I got the Sniper on the first attempt trying to beat the points threshold and I didn’t care about the exclusive. I was simply trying to upgrade the Solstice helmet to masterwork by beating the threshold. So, it varies for everyone. You can be extremely lucky or unlucky. Most likely, the one you want the most will take the longest. Somehow, the game just knows...