There's several ways that you could end up in a sniper duel that lasts less than a half second. The obvious one is the other guy is just good, lol, but let's discuss other more helpful ideas.... If it's a flat map with a lot of corners, good snipers know to line up their sights on the corner at head height in advance. The instant you step out BAM! So be mindful on maps like pantheon where the terrain is relatively even. Also you should be conscious of your own sniper glare; once you ADS you're very noticeable. Try to pre align your sights before you scope in. Try to center the screen on your target before aiming. This doesn't mean you have to quickscope, it just means to be more prepared before you initiate the fight.