Max roll on Damage Rating is calculated at 383 (382.9) for reg and cosmic, though I'd prefer to see an actual max roll. It's roll is tied 0.954:1 to the Reveal enemies roll based on these data points:

381/1598 Cos
376/1593 Cos
362/1579
248/1459 Cos
205/1414 Cos
192/1400 Cos

Dropps as cosmic arti from Stark Sentinel at the cosmic Danger Room trainyard scenario.