5.56mm x 45mm DU (Depleted Uranium)
The round is inherently based on the 5.56mm x 45mm NATO cartridge, and using depleted uranium rounds in the place of lead one's, to enhance armor penetration and increase the weight of the cartridge, thus increasing it's potential stopping power via momentum and inertia. The cartridge also uses more of a much higher pressure gunpowder, similar to that found in the 6.5mm Grendel and 6.8mm Remington to achieve it's effect, to increase the total energy of the cartridge. While a standard 5.56mm has approximately 1800 joules, the cartridge has roughly 3,000, making it's energy much higher. Furthermore, it uses an 8.5 gram cartridge, which is much heavier due to the use of Depleted uranium. The cartridge has nearly 65,000 PSI, far above the standard safety limit of 55,000 PSI, which means although the case is similiar to a standard 5.56mm, it will not work in the same firearms. Furthermore, due to the slight difference in the case (based on the 6.5mm Grendel cases, designed to feed in to 5.56mm weapons), they are not backwards compatible in the same firearms; they can be fired from the same barrels, however, and will work in break action or single shot weapons. The cartridge case is simply too different to feed reliably in a standard 5.56mm weapon.
Functionally, the cartridge is almost identical in size, shape, and velocity to the Mk. 252 cartridge. Because the depleted uranium is 70% denser, the cartridge than goes from 5 grams, to 8.5 grams, replacing the lead. Despite this, the cartridge still possess a similiar copper coating and a handful of other features, meaning it is not a direct conversion. The depleted uranium is much harder and tougher than lead, giving it superior armor penetration capabilities. The reduced velocity and increased weight of the cartridge somewhat reduces it's armor penetration abilities in relation to regular armor piercing 5.56mm rounds, however nonetheless it's higher energy puts it at roughly the same level (capable of penetrating 10mm of steel at 200 yards). The cartridge is substantially more powerful, with a bullet heavier than that of an Ak-47 traveling much faster, giving it much more stopping power. The depleted uranium is almost mixed with a small amount of lead and steel, which makes it somewhat softer, so it will deform more readily in soft tissue. The cartridge has the advantage of possessing a hollowpoint and being extremely accurate, equivalent to the Mk. 252, while also retaining the armor piercing ability of a standard round. It's energy range is between that of an intermediate and full sized cartridge, making it a somewhat
Depleted uranium was chosen due to it's plentiful nature (a by product of uranium processing), and it's reduced toxicity when compared to tungsten. Despite being very similiar, tungsten is more brittle, and additionally a somewhat more dangerous environmental hazard. Despite the alarms of depleted uranium's association with much more radioactive radioactive substances (such as U-235), depleted uranium is only weakly radioactive in comparison to most objects, and furthermore it's radiation is mostly alpha particles, which can't penetrate the skin or deeply in to sensitive areas of the body. Seawater, background radiation and granite all produce more radiation, and tungsten possesses a much higher chance of causing cancer if exposed. As a toxic metal, it is much more dangerous than it's radioactive effect, however this is in general less so than other heavy metals, zinc, lead, and the like. For all intents and purpose, it is in many ways safer than even lead, the most commonly used metal for bullets in general.
