The Assault Rifle Piercing Mod I has the following description which I find somewhat confusing:
Allows bullets to pierce 0.50-meter thick objects, but at 60% reduced damage. Ignores 25.00% of defenses on armored targets.
So, does this reduce my damage to 60% in exchange for armor-piercing, or does 25% of my damage go straight to health, but of that only 60%? How does this work with enemies that have just an armor bar and no health bar like Brutes?