"Sorry, but I can't. I have to take it with me while I go out hunting down some bastard who's been shooting people all over the DC area. Haven't you heard?"
BTW, anyone who allows the ATF to "test" their gun is a damned fool -- there's nothing that would prevent them from framing you for the crimes.
This may not be a coincidence.
Indeed. They're under pressure to find the perp. Look at the way the FBI has treated Hatfill.