there's no possibility it only does $300MM WW; unless you meant $150MM US + $300MM int'l which seems like where's it's headed.
Depends -- International take so far is below the U.S. domestic (at $56.5 million), so that's entirely contingent on which international territories it's opened in, & I don't know.
Forbes' Scott Medelsohn is now predicting it will track a la Thor 1 (which I had called 4 months ago) and finish with $156 million domestic / $390 million total (ww). I think the total international haul may be significantly less than $390.
http://www.forbes.com/sites/scottmendelson/2015/07/19/box-office-ant-man-opens-with-tiny-58m-weekend/
Interestingly, it's actually done worse than Hulk -- when adjusted for inflation & 3-D prices, Hulk actually did the equivalent of $70 million its opening weekend in today's dollars.
I'm not trying to be a naysayer; rather, my concern is how it effects the slate of potential unannounced films for other lesser-known Marvel heroes.
If Ant-Man significantly under-performs expectations, Disney will have to a) reduce the budget for new films featuring more minor characters or b) delay and/or cancel them altogether.
it's only opened in 1/2 the Int'l markets and is doing better than Cap 1 which did $195MM and bupkiss from China. i'll be the naysayer, i think already think a few movies on the in-production list will never see the light of day. shazam, black panther - wouldn't be shocked if those never get made.
Shazam will get one kick at the cat due to the Rock being in it. Some of the other spin-off movies with lesser characters will likely not see the light of day, though, if the others "falter". I can see 2nd and 3rd tier characters being added to team movies anchored by the big guns, but as solo flicks it will be tougher.
That being said, as long as the movies are clearing $400M worldwide they will likely keep on being churned out. Even if the total production and marketing cost is $200M, there is plenty of $$$ to go around after the fact. FWIW, the timing for the release of Ant-Man was terrible - launching a 3rd tier property in the middle of summer vacation? They should have switched the AoU and Ant-Man release dates as an Avengers movie will do well no matter when it isreleased.