NYC has plenty of BS rules when it comes to disposing of guns, almost all of which have to do with registration.
If you live outside of NYC, you can ship a longarm directly to a dealer in another state. Since handguns are registered directly to the owner, you have to take them to an FFL to have them removed from your license, since the people who manage the pistol permits (NYPD, NCPD, County Sheriff, Clerk, etc.) need proof that the weapon was properly "disposed of".
This is one of my biggest gripes about NYS pistol registration laws. Why should I have to go to a dealer to have him ship a gun for me when I can do it myself? The only benefit I see is that a dealer can legally ship handguns via US Mail (by filing some form with the post office when they mail it). FWIW, I would rather send it Fedex and pay the extra cash to make sure it gets there without the box being opened.
MJ