Props to sSantzuu here, who does some major work with his sidearm in the video above—look at how he takes down a chopper at long range. Crazy stuff.
Sniping people with things other than sniper weapons is definitely one of my favorite things to do in Battlefield games, so I imagine pulling this off must've felt fantastic.
Update: Ah, as the "anti-explosives" ribbon suggests, the chopper may have been rigged with C4 in an attempt to capture the shot. An impressive shot at that distance nonetheless!
Battlefield 3 - Epic magnum snipe [sSantzuu]