The M90, minus SP90E1 suppressor.

The M90 is the standard-issue long arm for Colonial Marine Vent Infiltration Specialists, highly-trained soldiers who are capable of infiltrating and moving through ventilation systems on hostile ships, space stations, and ground buildings, and who are nicknamed “Vent Rats”.

Weapon Designation:Personal Defense Weapon, 5.7mm, Caseless, Pulse-Fired, M90
Type:Personal Defense Weapon
Place of OriginBelgium
In Service:2055-present
Production History:
Manufacturer:FN Herstal
Weight:5.7 lb (2.6 kg)
Length:19.9 in (505 mm)
Barrel Length:10.4 in (264 mm)
Cartridge:5.7x25mm Caseless
Action:Straight blowback, electronically ignited cartridges
Rate of Fire:900 rounds/min cyclic
Muzzle Velocity:2,488 ft/s (728 m/s) with M5-731 round
1,017 ft/s (310 m/s) with M5-755 round
Muzzle Energy:426 ft/lbs (578 Joules) with M5-731 fluted round
126 ft/lbs (171 Joules) with M5-755 fluted round
Effective Range:200 m (218 yd) with M5-731 round
50 m (55 yd) with M5-755 round
Feed System:50-round detachable box magazine
Sights:Iron sights, laser aiming module


Although the M24 pistol was designed to be the primary weapon of Vent Rats due to there being little perceived need for a larger weapon like the M41 submachine gun, there were some scenarios where Vent Rats did want to carry a weapon that was more powerful than the M24 while still being smaller and lighter than the M41. In response to requests made by these personnel, the M90 was developed in the mid-2050s. The FN Herstal P90 was selected because of its compact, lightweight design, although two changes were requested: the addition of an electronic firing system and a switch to caseless ammunition so that an operator firing their weapon in a vent would not have to deal with hot casings bouncing around inside the vent.


From the outside, the M90 is nearly identical to the basic P90. The primary differences are internal, with the use of caseless ammunition and an electronic firing system instead of a hammer-fired trigger pack. This requires some care to prevent the weapon from overheating and also means that the operator must be careful not to expose the ammunition to any type of contamination which could ruin the ammunition and cause the gun to malfunction. The M90 still has an extractor, ejector, and ejection port for ejection of a failed or training-use round.


The M90 has two different sight systems. The first is a set of low-profile iron sights, while the second is a dual-mode laser aiming module, with power buttons on both sides of the frame under and ahead of the charging handle. The right button activates a visible laser, and the left button activates an infrared laser that can only be seen with night-vision goggles.

Range, Accuracy, and Terminal Ballistics:

The 5.7x25mm caseless cartridge used by the M90 has virtually identical performance to the cased 5.7x28mm round that the basic P90 fires and as such, its terminal performance has remained somewhat controversial among misinformed or uninformed users. However, official testing has repeatedly indicated that just like the 5.7x28mm round, the bullet of the 5.7x25mm caseless cartridge consistently tumbles end over end in a soft target, dealing significantly more damage than a conventional pistol cartridge of a larger diameter. However, the 5.7x25mm round’s wounding capacity is not superior to or even equal to the wounding capacity of explosive variants of more conventional cartridges like 9x19mm Parabellum.

There are two cartridges used by the M90: the M5-731, and the M5-755. The M5-731 is the equivalent to the 5.7x28mm SS190 round and is capable of penetrating a Level IIIA Kevlar vest while still retaining sufficiently lethal wounding capabilities. It is officially listed as effective out to two hundred meters, although some users have reported effectiveness at up to three hundred meters.

The M5-755 round is a subsonic cartridge intended to compliment the SP90E1 suppressor, which is used by Vent Rats. Its subsonic nature results in significantly lower muzzle energy and far lower effective range as a result. However, it is still effective at up to fifty meters, more than sufficient for the needs of Vent Rats, who operate mostly in vent systems and the close confines of buildings, ships, and space stations.

Additional Accessories:

The M90 has only one notable accessory, the SP90E1 suppressor. This 1.6 lb suppressor is 1.5 inches in diameter and 7.2 inches long and attaches in place of the standard flash suppressor. It is capable of reducing the weapon’s sound signature by 47 dB when used with subsonic M5-755 ammunition.

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