Hm.
Well... it's kinda embarassing how you put "Moive Loading" on the first screen. As for the acctual Navy SEALs, they are not "the best" snipers in the world. I doubt there would be a single way of telling who was "the best" at anything. Each government has their own secret forces under their command... not to mention all the terrorist factions out there that are very good at what they do. In order to base a claim like that, you would have to round them all up and have a contest. Not too likely. I don't think there is any basis for the claims made in this movie.