M99 Stanchion rifle (Earth-5875)

The M99 Special Application Scoped Rifle, also known as the M99 Stanchion Gauss rifle or simply the Stanchion, was an anti-materiel rifle used by the UNSC Marine Corps during the 25th century.

Design and operation
Much like other magnetic weapons, such as the Magnetic Accelerator Cannon and the mass driver, the M99 Stanchion works on a similar, but smaller-scaled principle. The system of the weapon works through a number of electromagnetic coils instead of chemical propallants to produce kinetic energy. Its weight and bulk make it difficult to use in long-range sniping roles, although it is quite deadly.

The M99 is used alongside a portable computer that provides its user with the necessary ballistic calculations that engage the rifle in long range operations.

Ammunition
The M99 uses the small 5.4mm/.21 caliber, which, while small to other rounds used in multiple weapons through the Secession, it served in conjunction with Gauss technology, allowing it to pierce entire targets apart, even through building and titanium. Upon impact, the round creates an explosive shockwave. While hitting material, the shockwave results in a minor explosion that cause structural fractures, while in personnel it rips and pulverizes the body around the impact area.

The 5.4mm/.21 can travel between massive distances without having its trajectory affected, and once it impacts, it gives a blow ig enough to punch through instacrete, blow a human, and continue on its course.