Drill Rounds are a relatively common form of caseless, HEIAP (High Explosive Incendiary/Armor Piercing) ammunition designed by humans. They are essentially oversized flachettes, fitted with a depleted uranium tip (itself coated with magnezium), and filled with an HE charge and zirconium. The end result is a round that pieces thick armor before detonating moments later.
Drill Rounds were developed in the final third of the Human-Taik War as a means of breaking through their otherwise inpenetrable double-layer of armor. Production for human military use was halted by the H.O.A. They are also quite popular in galactic black markets, notorious for their keen stopping power and armor piercing capabilities. Their use on unarmored targets is very controversial, often stated to be on the level of a war crime. This is somewhat justified, as the wounds they can inflict can be very gruesome.
Drill rounds are basically large spikes (typically about 7 inches long) made of hard materials such as tungsten or even titanium. They have barbed tips made of depleted uranium that allows them to pierce straight through armor of incredible thickness. The tips are also coated with a layer of magnezium that ignites on impact. This activates an internal HE (High Explosive) case, which, in turn, activates a second, zirconium-based, explosive. Zirconium burns at an extremely high temperature, and its fires are known for being difficult to put out. This mixture of pure kinetic force and white-hot burning is what gives drill rounds their notorious power. If the rounds cant outright pierce through arrmor, they will embed themselves into it and detonate, severaly weakening it (on top of the zirconium effectively melting through it).
The flachettes are cased inside a solid mass propellant complete with a combustible primer. When the weapon is fired, the primer ignites with tremendous ferocity, propelling the round to super-sonic speeds. The muzzel velocities tend to be so high that the rounds leave behind a visible smoke trail. While this does give away the shooter's position, the rounds themselves are hardly subtle.
Most non-human weapons are incompatible with drill rounds, and have to be modified in order to handle both the hefty weight of the rounds, and the immense recoil experienced when firing them.
Drill rounds were used extensively during the end of the human-taik war, during which they proved very useful against the thick taik armor. While they faired better than conventional rounds, however, the taik quickly answered by simply using thicker armor (up until this point, they had been using the lightest armor in their arsenal). Nonetheless, the drill rounds were still able to heavily damage whatever armor was thrown at them.
Following the conflict, they have found little practical use. When facing infantry or vehicles they are essentially overkill, and in space they are insuccifient when compared to the larger rail cannons used. Despite this, they have remained popular in anti-materiel roles. Beyond this, they have been largely replaced by more conventional armor piercing rounds.
Drill rounds are strictly regulated by galactic governments, and generally only military forces are permitted to use them. However, this has not stopped black markets from selling them in large quantities for high prices. They are very popular with mercinary and pirate groups, largely due to their near unstoppable nature, and for their use as psychological warfare (death by impalement).