* Part Damage
HOW THEY GET PICKED
For this list I went through each weapon's attachments and gather the ones that have positive Damage or Part Damage (limb multiplier) perk, or have positive Damage stat change.
I then sort the attachments from highest to lowest, then collect the highest Damage change for each attachment type.
BK57 is the only one with 0 damage stat change but includes Part Damage in the attachment's pro list.
Note that if 2 attachments in the same category have the same change, the first one in the attachment list would usually win out.