We pretty much expected that “Insidious: Chapter 2” would top the box office this weekend, but it still managed to exceed expectations by scoring the biggest September horror opening of all time and the second-biggest September opening for any genre (trailing only Hotel Transylvania’s $42.5 million), with an estimated $41 million. By comparison, Insidious opened with $13.3 million and James Wan’s “The Conjuring” opened with $41.9 million in July.