Talk to Abraham Washington and head to the National Archives. Agree to work with Sydney, keep her alive for the original attack to save loads of time by going down the elevator (Going the long way only gives you generic loot and drastically decreases your life expectancy). Then, after shooting or speech challenging Button Gwinnet, kill Sydney for menial bad karma, (or upset Button and hide behind Sydney so she gets killed by the turrets) and land yourself a unique gun and some reasonable armour, plus no reward sharing. And this quest can be done in about 5 minutes ater stepping into the place. Easy.