If you remember, the bump stock ban going into effect was premised on the Las Vegas mass shooting at a country music event. If you believe the official story, a single man holed himself up in a hotel room with literally dozens of guns, several phones, and at least one laptop with a missing hard drive, before using his elevated vantage point and some of his firearms to shoot into a crowd. By the time police worked up the courage to enter his room, he was dead -- supposedly by suicide.
The firearms he supposedly used to shoot into the crowd were also supposedly fitted with bump stock devices. The ATF subsequently used that event as justification to make a rule change banning bump stocks by considering them to be machine guns -- a rule change that violates the plain language of the law.
To be sure, there are other possible reasons the FBI might not allow the ATF to examine the guns. A few that come to mind: did the shooter have ties to law enforcement or intelligence agencies that might have shown up if the guns were examined and (especially) their serial numbers traced?
Some people will call this a conspiracy theory. They said the same thing about the idea that the FBI were listening in on the Trump campaign, and look how that turned out. I'm not claiming to know what happened or saying it was all some sort of plot. But is it too much to ask that government agencies tell the truth, stop hiding information, and stop taking advantage of public crises like this one to advance their so-called national security policies through fear?