If you press X in the battlepass screen, it actually lists all sources that you can get xp from. It lists looting metal parts and wire as giving xp but not for retrieving, so it appears to be an intentional choice made by the developers.
There appears to be a bug when firing the m2 while it's set to full auto that removes all recoil. After firing 3-5 bullets the gun just stops having any recoil whatsoever, even after you stop firing or after you reload. The recoil returns after you move the reticle, but moving your character without adjusting your crosshair allows you to maintain the effect. https://1drv.ms/v/s!AsdgP-3dH6y-dkYbV0pRP2SHycI