don't know if this was a real story, but I seem to remember a story of a sniper team in either the first Gulf War or the invasion of Iraq who used the .50 Barrett to take out not one, but two BMP's... As I remember it, the sniper hit the first one disabling it so heavily that the second one's crew all jumped up and surrendered!
And I seem to remember that part of that story is that it was out at a range of almost a mile...
And, the record for a distance kill, if this story, too wasn't a fabrication.... was from a Canadian sniper who took someone out at well over a mile... but it took him like three shots to hit the guy..
All's I know, it'd be too dang expensive, heavy and unwieldy for the criminally inclined to bother with...