Nunu Ult Bugged?

Didn't catch a screenshot of it, but I got into a ARAM as him and his ult did the full damage if completely channeled without a problem, but I got to around .5 seconds left of the channel (almost done) and it barely did the base damage (base was 180ish, hit for 150ish).

Did I miss a change where it's less rewarding for a decent time on the channel or is it bugged?