High Explosive Dual Purpose ammunition
From Halopedia, the Halo wiki
HEDP ammunition, as the name suggests, is a form of ammunition designed to explode on impact with a target or other object. HEDP ammo is known to come in at least 12x99mm, due to its operation in ONI-specialised M343A2 chainguns.
HEDP ammo is not commonly employed by standard UNSC forces, but is instead employed utilised in select deployments. The Office of Naval Intelligence's own security forces in particular make heavy use of HEDP munitions. HEDP ammo is employed via way of the M343A2 chaingun, in both regular turret and vehicle-mounted configurations. Known vehicles employing HEDP ammo include;
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