the 6P62: Crazy!
Wow. Saw this gun on Wikipedia and thought its strange...
Anyway, if you don't know what a 6P62 is, heres some background: It's a Russian Hand Held Anti Material Rifle chambered for the 12.7x108 mm. It holds 14 rounds in it's giant magazine and can pierce through 20 mm of steel. about 400-500 rps.
For some imagination fun, how about this: when replying to this, say what a person would look like after being hit by one of these. That guy on the bottom has nerves of steel to fire this!
(oh yea almost forgot. it can be attached with an rds, seeing the picture below.)