ISIS' premier round, that which both the AZ-56 and GZ-159 SDS-MP weapons systems were built around. It's a medium round with a heavy charge, and a long bullet by modern standards.

The labels are as follows.

5.9x40mm Z21 "Ubiquitous" Si vis pacem, para bellum.

-Jacket
-Tip(hollow)
-Lead plate, "tumbler." Breaks jacket.
-Spacing(hollow)
-Core, S3. W(sub2)C(Tungsten Carbide)
-Core casing, "splinters".
-Core, S2. HRC 62 Steel. Special use variants :
--Z21-B holds explosive charge, phosphorescent.
--Z21-C holds chemical charge, 2-stage [high heat reaction].
-Core, S1. HRC 60 Steel.
-"Molar" cavity. Point of discharge force.
-Explosive propellant, S2.
-"Echo" breaker. Explosive guide, light composites.
-Explosive propellant, S1.
-Primer

A secondary export variant exists of the Z21, known as the Z21L, that contains no Tungsten Carbide for cost or rationing purposes. The Z21 is designed as a proprietary, special purpose round for use in a special-needs capacity. It's designed for heavy penetration and rupture on entry.

All names and information related to are trademark of ISIS DFC, ISIS Metalworks, ISIS Global, and their subsidiaries.