I haven't seen any videos on this and am not really sure if it's already known but I wanted to make a video on it.
Attack stacking basically allows you to register 2 hits in the time it would take to do 1. Attack stacking is done by attacking, swapping weapons immediately, and attacking again. This allows you to output damage much faster than waiting on your weapon to fire again on it's own.
Sorry if this video seems out of place from my normal stuff but I used to play FusionFall when I was 10 years old and in 2013 the game was shut down. This is FusionFall Retro which is a reboot of the game that recently got a big update that contains most of what the game was and I've started playing it again for nostalgia.