This is a Maverick Article
Plasma cased munitions or PCM are micro-projectiles cased in a plasma field generated by ions stored within the weapon system. The Projectile is surrounded in a plasma field and propelled with rail gun batteries within the weapon system. Upon impact the projectile deals both energetically discharged plasma and the kinetic impact of the projectile itself. PCM rounds do both plasma damage and kinetic projectile damage to targets making it ideal and versatile on the battlefield against a range of targets.
PCM rounds were created by the Concord of Humanity in 2607 in response the ever changing conflicts in the aggressive galaxy they now existed in. PCM rounds allowed soldiers of the Concord to combat many forms of advancement successfully.
It is widely understood that a species reliant on projectile based weaponry has defenses and utilizes materials which are resistant to the very weapons they employ. This is seen in the way Covenant armor was susceptible to Mass Accelorator weapons employed by the far less advanced UNSC. Similarly Covenant plasma weaponry burned through UNSC conventional armor with ease. On the ground the UNSC forces had the advantage over the Covenant due to the Covenants lack of adequate defenses against mass accelerator weaponry and non-energy based weaponry. Meanwhile human starships would be torn apart and melted into twisted chunks of space debris by the overpowered plasma torpedoes and energy projectors which the UNSC had no defenses against.
PCM rounds could easily combat a plasma-savvy enemy with the kinetic damage dealt by the round along with the system damaging affects of the plasma casing being released as a micro EMP burst upon impact. Similarly against an enemy employing kinetic based weaponry, the plasma shielding around the projectile would melt down enemy armoring giving the kinetic round a deeper penetration level.
Most weapons used by the UNSC and now CoH were easily modified to be PCM capable with the rise of profound technological advancement. Even MAC guns on ships and stations employ PCM technology.