The SFL-4 fires a tight cluster of 24 steel micro-flechettes from a rotating drum magazine, each flechette coated in a piezoelectric polymer that activates on deceleration within soft tissue. The flechettes themselves are not individually lethal — each is 1.8mm in diameter and 12mm long — but the cluster dispersal pattern, combined with the piezoelectric activation sequence that fires as each dart decelerates, creates a cascading internal disruption effect that is grotesquely effective against unarmored targets. Against light armor, the flechettes lack individual penetrating power, but three or four cluster shots against the same panel can compromise soft armor integrity enough to allow subsequent rounds to penetrate.

Zheng-Dao Bioelectric's engineering rationale for the piezoelectric coating was ostensibly medical — the activation signature was derived from research into internal tissue stimulation for nerve damage treatment. The SFL-4 was developed under a security applications contract that repurposed this coating for terminal ballistic enhancement. What distinguishes it from conventional flechette weapons is the sequenced disruption cascade: the flechettes do not all activate simultaneously. The deepest-penetrating darts activate first, creating an internal pressure wave that the shallower darts then amplify, producing a disruption effect far larger than the physical volume of the flechettes would suggest.

The weapon's design is deliberately compact — it resembles an oversized semi-automatic pistol with a wide, cylindrical magazine housing — and it is deceptively light for what it does. Operators describe the firing experience as anticlimactic: a soft pneumatic 'pop' and then the target's reaction to 24 piezo-activated micro-darts is rarely anticlimactic at all. The SFL-4 has a disturbing reputation in field medicine; the flechettes are extremely difficult to locate and remove without specialized scanning equipment.