How can I add an augment to my weapon?
Solution 1:
Slots for augmentations only appear on higher level versions of items.
Augmentations are added during the development of the item by selecting the augment slots in the same way as you would when adding mods on the load out screen:
Solution 2:
Most weapon at lvl 2 got augmentation slot. The first lvl for all weapon do not have. You will need to research the second lvl for that rifle.