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M99-S2 Stanchion
Xie R30
M99-S2 Stanchion without stock and power source

Place of origin:

UEGSeal Unified Earth Government


Anti-materiel rifle

Service history

Used by:

UNSC Defense Force


Post-Covenant War conflicts

Production history


5.4×62mm AP

Muzzle velocity:

15,000 meters/second

Effective range:

4500 meters

Feed system:

10-round detachable box magazine


The M99-S2 Stanchion, like its predecessor, the M99 Stanchion, is an anti-materiel rifle that incorporates coilgun technology to fire projectiles at incredibly high velocities. As an anti-materiel rifle, the M99-S2 is intended for deployment against military equipment, neutralizing such assets from very long distances. The M99-S2 can also be used effectively against a wide range of other targets, such as vehicles and personnel.

Design details

As a successor of the M99 Stanchion, the M99-S2 Stanchion uses the same technology as that of MACs, except on a much smaller scale. The M99-S2 uses a series of electromagnetic coils instead of chemical propellants to accelerate its projectiles at up to 15,000 meters per second.

Like its predecessor, the M99-S2 must use an external power source in order to be fired, due to the amount of energy required to magnetically accelerate projectiles up to many times the speed of sound. Unlike the M99, however, the M99-S2 is available with a portable battery pack that can be worn on the back of a SPARTAN wearing MJOLNIR armor. This allows a SPARTAN to use an M99-S2 for extended periods of time without having to remain at the same location.

The M99-S2 features a bipod as well as a holder for a spare magazine installed right in front of the trigger, behind the active magazine.


The M99-S2 is chambered for caseless 5.4×62mm 272-gram rounds that each and possesses a depleted uranium core coated with ferric tungsten. The immensely high velocities of projectiles that come out of weapon's of coilgun technology shreds infantry targets apart and creates explosions on a materiel targets.