· I heard that sales cannot be recorded in any format that is "searchable," so many records are kept on paper. When police have to track down a firearm used in a crime, they make phone calls to dealers, who sort through files. If this is at all true, it is surprising that any firearms are ever tracked.

At 17 I purchased an SKS from a guy in a trailer. I wrote my name down on list. The list went into a box. The box went into the trailer. I think the guy asked to see my driver's license. He wrote down no information. When I asked him what happened to the box he said "if the government ever produces a court order, I'll give it to 'em after I set it on fire."

When I moved to Washington I inquired with the Seattle PD if I needed to inform them of my guns. They asked why I would do something like that.

· This probably varies by state, but I understand that the "gun show loophole" has nothing to do with gun shows. Licensed dealers are required to do background checks before a sale, but anyone else can sell firearms without background checks. Is it really legal for someone to sell a handgun to a total stranger for cash? What other criminal charges might apply in such cases?

wikihow has ten steps to your FFL. note that these are slightly less stringent than the steps necessary to legally draw blood. For background checks, see above.

· What are the rules about modifying firearms, like filing serial numbers or sawing off barrels?

A sawed-off shotgun is specifically called out as a Title II weapon of the National Firearms Act. Title II includes shit like full-auto machine guns, hand grenades, weapons over .50 caliber (excluding barrel-loading black powder weapons) etc. The act of turning a Title I weapon into a Title II weapon (by, for example, converting a semi-automatic rifle to fully automatic or select-fire) is a federal felony.

It was this very act that an undercover agent hired Randy Weaver to do while they were sitting around drinking beer. The agent did so in order to leverage Weaver into informing on the white nationalists in Sand Point. Everything went worse than expected.

· Silencers. Apparently very unlike James Bond depictions, and more useful to protect the shooter's hearing than for getting away with a stealthy kill.

There are two acoustical noise sources that need to be ameliorated: the percussive expansion of exhaust gas and the sonic boom of the bullet breaking the sound barrier. A suppressor has no effect on sonic booms whatsoever. However, exhaust gas can be baffled relatively effectively, particularly if you've got the room for a decent baffle. It's possible to shoot spooky quiet if you are using subsonic ammunition.

Most calibers, however, are supersonic, and most of what you see in film is synthetic foley that has never been anywhere near an actual firearm. Guns are a bitch to record up close because their soundwave is a single percussive discontinuity well above the dynamic range of any mic you would use to capture the early reflections and tails that we psychoacoustically characterize as gunfire. A legitimate silenced weapon, meanwhile, mostly sounds like a dry fire.

There are several scenes in "Heat" in which firearms are used inside vehicles. Permanent hearing loss, or only temporary?

Percussive hearing loss occurs in a whole 'nuther regime than OSHA noise exposure and is nonlinear. Will you be deaf forever from shooting in an enclosed space? No, but that ringing in your ears is the cilia within your ear canal dealing with damage. Every time you damage them fewer recover. Eventually your high frequency hearing goes away. I used to go shooting a lot, with ear protection, using my buddy's guns. His dad had been shooting for so long without hearing protection that he could no longer hear the phone ring.

Those guys occupationally fired large caliber weapons within an enclosed space. Their hearing likely suffered, but not so fast that they were one and done.