Christine" feigns fear that the gun he is holding was not one of the "prop" guns that the CRS Security Guards carry, implying that this was a gun that Van Orton owned that CRS didn't know about and thus wouldn't have been able to "fix." They knew about the gun all along; the State of California is incredibly restrictive in their gun laws and any firearm that a private citizen purchases is on record. With CRS's many contacts and key players in influential positions, they were likely able to discover the record of his handgun and, during their reconnoiter (and eventual ransacking) of his home, found it and replaced the live rounds with blanks (which can still kill; when Van Orton was holding the gun to "Christine's" head, the tremendous pressure created by the expanding gases caused by firing a blank would've been more than enough to kill her at that range). Purchasing a new firearm in California is also very difficult, with background checks, paperwork and a waiting period; likely CRS would've been alerted had he attempted to purchase a new handgun. Though if Van Orton were initiate in firearms (which he doesn't seem to be [CRS would've discovered all this during his "exam"] as demonstrated by the manner he holds the "PI's" gun after his house had been burgled), he would've checked to see that the gun was loaded and, with all that had happened to him creating such incredible paranoia, checked the rounds to make sure they were live. CRS would've been in big trouble if he had another box of ammunition or kept the (loaded with live rounds) gun he took from the "PI". Let's just say that this movie wouldn't work if set in Texas or the like.