That's because you (and many others) are setting these up wrong. It's not your fault really. Bungie made it somewhat confusing. Ill try to be quick here: The card doesn't need to exceed a B+ (it should visually look like B+ and about 3/4 on the bar) for A rewards. Your final score determines the letter grade, and there are 2 things that grant extra score in an activity: The side objective (20 precision kills or whatever) and finishing before time runs out. Do both, every time. I'm going to give an example of what I ran today. Caldera Solo Ops: Choose a Bane modifier, this is a must, gives the most score multiplier Choose the major (not the minor)threat mod (arc, solar, or Void and put on the resists to compensate) Select the " no starting ammo" mod(you get free ammo boxes in the activity) Now Select 2 +10s of your choice You should be now sitting at a total of a -30. As long as you use featured gear, which i see you are (I use an exotic class item like you) run it, do the side objective and beat the time (which is easy to do), boom, A rewards. If you end up shy on the score, add another +10 or whatever you need to make up the difference. You shouldn't have to ever be beyond a -40 for A scores below 450. Hope this helps.

Diarrhea is a problem.

Same here. Extremely frustrating. I thought Bungie said it was going to be a faster power progression from 400-500, and from 500-550. I'm at 425 and I can't get a prime drop after doing all the solo portal activities. I tried fireteam ops and nothing to help with the progression.