http://en.wikipedia.org/wiki/Simo_Hayha
Simo Hayha, with 505 confirmed kills during the Russo-Finnish War, is recognised as the highest-scoring sniper of all time. Now, WI after WWII he'd taken a similar route to Larry Thorne by migrating to the US to offer his services to either the Special Forces or USMC as a sniper ?
Simo Häyhä's kills have been exaggerated by all accounts, he was propagandized on purpose. Confirming kills in sniper activity is always difficult but in special conditions of Winter War (with problems such as darkness and snowfall and the fact that kills were made in midst of major battles) especially difficult. However, the man was excellent sniper by all accounts and used a number of innovative tricks. First, he used normal infantry rifle with iron sights for lower shooting profile, no possibility of glare and no possibility of singling out the sniper. Second, he froze the snow in front of him with water, eliminating the "puff" which comes when firing with a rifle near snow. Third, just before shooting he ate snow to eliminate breathing steam.
He was severely wounded during the war and while the methods were innovative I think they could be learned by any skilled sniper. Like Finland, US has had it's portion of natural snipers thanks to widespread hunting.