Yeah I think sniper rifles should be 1-hit kill most of the time. Even with heavy armor. Another solution would be to make someone slow down significantly or fall down when they get hit. Wearing armor, a round as big as .308 or 762x54R should at least put you on your ass with the wind knocked out of you and multiple broken ribs.
This was a problem with damage registration which was supposed to be fixed in today's patch.
Fixed an issue with bullets where damage dealt could fluctuate from intended values, improving reliability of bullet damage calculation.