What I need is a gun, easily obtainable (and preferably not military-issue) that can fire (either to wound or to kill) from the London Eye to 10 Downing Street. The distance is approximately a quarter of a mile. I can have gravity do most of my damage for me, but I DO need something that can fire a bullet (or series of bullets) that would make it that far.
No, I'm not planning to shoot Tony Blair ;)
Help much appreciated.
Edited for slight retardation. Thanks for the help, though. I'll figure something else out :)