Shredder rounds are special rifle cartridges designed to expand upon entering a target in order to decrease penetration and disrupt more tissue as it travels through the target.
In terms of performance, shredder rounds would function similar to a jacketed hollow-point ammunition. The bullet consists of several segments of a hard metal that is welded together with a soft metal such as lead. The welds acts as weak points, so that on impact, the bullet should separate along the welds into component segments. This spreads the damage over a larger area, but it also decreases the penetrating power. These rounds are surrounded with a fluted or perforated metal jacket in order to provide optimal fragmentary habits, as opposed to a haphazard disintegration which would do less damage.
Magnetic Accelerator Cannons can also be equipped with a round that acts similar to a shredder round. The UNSC Pillar of Autumn was the only known UNSC ship to be armed with this type of MAC ammunition.
They were used by SPARTAN-IIs of Blue Team after exhausting all of their AP rounds when gunning down a horde of Unggoy in the defense of Jericho VII. Another instance is when Blue Team is at Cote d'Azur, engaging a pair of Hunters in a museum. After discovering that the AP rounds were ineffective against the Hunters' armor, the SPARTAN-IIs resorted to using shredder rounds and fired at the marble floor beneath the Hunters to immobilize them.