I totally understand your reservations. It can truly go either way. As I've said before, the box office is unpredictable.
Imo, though, the only way this falls short of that number is if the reaction from critics is like it was with Fantastic Four last year. As soon as the reviews came in, that movie was dead on arrival. If this movie can avoid that fate & turns out to be good or great, it could hit those numbers.
But if it is great, expect word of mouth to spread like wildfire and for this to break out. If not, it'll be a long, long time before another R-Rated superhero movie surfaces.