Bear with me for a second.
Guns of Icarus is actually a sci fi, futuristic, space fighting game and we're in the middle of what is basically a really long easter egg sort of joke. Most things in the game were transferred well over into steam/diesel punkiness. However a big part of the gameplay mechanic was shields which you obviously can't have in the era. So they changed the name from shields to armor and kept everything the same.
Think about it, what is the best way to destroy the "armor" in this game? The machine gun. Any scenario where shields are involved its always the many weak shots that are effective against shields. Generally those are ineffective against armor.
Think about it man, its a conspiracy!