Specific frame types, anatomically aware scope and feats in case of guns.
Reaper sniper rifle frame has 125% crit damage, anatomically aware scope adds a whopping 50%, Sharpshooter feats adds another 30%. So it's 205% total.
Crititcal power feat gives you additional 1.5% crit damage for every 1% above 100% you have, effectively multiplying every point above 100% by 2.5.
So now it's going to be 100%+(105%*2.5)=100%+262,5%=362,5% critical damage, but for some reason the game rounds it to 361%.
Add a a good smart module that increases the damage of special attack by, say, 30%, and you get 361%*1.3=469% crit damage, so pretty much 4.5 times more than regular shots.
It can get even more ridiculous with plasma pistols as the amplifier mod increases crit damage, and with a really good one you can get 250%+ crit damage on the weapon alone. With all the feats it's possible to achieve 600%-700% crit damage with them.