How do I add Piercing 2+ to a weapon? Has this been overlooked?

As far as I know the Piercing effect stacks so that it’s possible to a weapon with Piercing 2 or 3. I can’t seem to find a way to add this to a weapon and under the damage effects, even though the laser rifle (piercing I) has the sharpshooter mod which should raise its piercing to II it isn’t showing up.

Any advice would be appreciated, thanks.

Edit: Opps sorry, I thought this was the Fallout Fantasy Grounds Unity forums.