The PGM-4 is a spherical micro-projectile designed for the CDP-2 'Bruiser' platform, consisting of a 4mm gel bead with an embedded piezoelectric crystal array suspended in a biocompatible polymer matrix. Upon impact with biological tissue, the bead deforms and the resulting mechanical stress activates the piezoelectric crystals, which generate a focused electrical discharge that propagates through the target's capillary network. The discharge is calibrated to cause localized vascular spasm and capillary rupture without creating a penetrating wound.

The bead's gel composition is the key engineering achievement. Helix Biosystems developed a polymer that is rigid enough to maintain ballistic stability during flight but deforms completely on soft-tissue impact, maximizing the piezoelectric activation surface area. Against hard surfaces — walls, armor plate, bone — the bead shatters without activation, producing no electrical effect. This material-selective behavior is what allows the CDP-2 to be marketed as a 'non-lethal' platform in certain jurisdictions, though the lethality at close range and on overcharge settings makes that classification dubious.

Each charge pack contains 22 beads in a sealed linear magazine with integrated propellant cells. The beads are nitrogen-sealed to prevent moisture degradation of the piezoelectric crystals, which gives them a shelf life of approximately 18 months before performance degrades. Expired beads still function as impact projectiles but lose their electrical discharge capability, reducing the weapon to an expensive pellet gun.