While an Absorb Shield is active, it has a set percentage chance of adding ammunition to the user's reserves when struck by bullets or rockets. When the shield absorbs a shot, it negates the damage and the character receives ammunition corresponding to the type of weapon fired by the enemy. For example, an enemy with a shotgun will give shotgun ammo if his bullets are absorbed.
As the rarity level (and therefore the material grade) of the Absorb shield increases, the Absorb probability increases.
In order for a projectile to be absorbed, it must be fired from a weapon the enemy is holding. For instance, a bandits/scavs with an submachine gun is a valid candidate for absorption. A WAR Loader firing autocannons is not. Furthermore, only the actual projectile can be absorbed and negated. Splash damage from explosive and elemental weapons will impact normally.
Certain weapons fire special projectiles that Absorb Shields treat as rocket ammunition. For example, the Boom Puppy, Landscaper, and Logan's Gun can all provide rockets when striking a character's shield.
It's advisable to equip an Absorb Shield when:
the environment offers little or no cover from attacks;
there are various enemies that attack using hand-held projectile weapons;
The Gunzerker uses his action skill, in order to maintain a firepower and survivability advantage in open combat.