M90/A3 (GAU-24) Squad Support Vulcan (Minigun) Cannon.
“Say what you want about how old an’ outdated the M90 is, it’s still the
best damn machine gun in the USCM. We were stationed on LV401. They
were having problems with the tree-huggin’ locals causing trouble with the
mining ops there. Our squad was on patrol and these greenies come outta
nowhere, throwing homemade Molotov cocktails. Jorgenson, our ‘gunner
with the M90, spun that heavy beast around so fast it’d make your head
spin! She fired, I shit you not, three short bursts of HEAP rounds from the
thing. By the time she spun down the barrels what was left of the ten or
maybe twelve greenies looked like piles of cooked hamburger.
Nasty stuff, man!
After that night the attacks stopped comin’ for some reason. Rest of our garrison detail was a frickin’ cakewalk…”
- Pvt. Jason “Red” Trump.
Prior to the introduction of the M56 Smart Gun, for nearly thirty-five years
the M90 rotary Vulcan (Minigun) cannon filled the role of the heavy support
weapon. Heavy, and durable to a fault, its ability to unleash a devastating
amount of firepower in a short time over a wide area has made it a valuable
addition to the USCM arsenal. With the introduction of the M56 weapons
platform, the M90 is being phased out of service in most branches, but
combining the M90 with the newer M56 support arm and harness has given
the weapon an extended lease on life.
The Navy and Air Force version of the M90/A3 is called the GAU-24 and
is dual mounted in turret assemblies. It’s expected that the M56 will
completely replace the M90 within 20 years as operating parts and
supplies for the M90 system are issued and not replaced.
GENERAL DESCRIPTION
The M90/A3 is a three-barrel, 10mm general-purpose automatic squad
support weapon, effective out to 1200 meters. The electronic pulse-action
firing system employs a high speed rotating block breech mechanism
chambered for the M245 series 10mm x 28 caseless HEAP (High Explosive
Armor Piercing) round. If deployed in civilian centers where collateral
damage is a risk, the weapon can also utilize the newer M250 variable
fuse caseless round.
The rotating three-barrel assembly has an adjustable cyclic rate from
1100 to 2,000 rpm. The M90 is factory pre-set at 1100 rpm for ammunition
conservation. The cyclic rate can be adjusted by a licensed armorer
at any USCM facility.
Ammunition is housed in removable 250, 400 or 950 round box magazines
attached to the weapon’s underside. Typical four-man patrol squad use
will see the weapon outfitted with the 400 round box. The 250 round box is
typically issued to patrols in civilian centers, and the 950 round box is
typically issued in high-risk garrison or combat operation environments.
The box magazine is an electric driven snake drive feeding mechanism with
UV/IR sensors that function even if fully submerged to provide flawless
ammunition feeding in all environmental conditions.
The weapon housing is constructed largely from molded carbon fiber and
alloy metal stampings while the main barrel assembly is machined from
high-grade steel and titanium alloys. The majority of the interior parts are
constructed from titanium alloys for lighter weight and long-term durability.
The three machine shop replaceable barrels are air-cooled. The M90
system predates the M56 Smartgun by thirty-five years. The weapon
uses the same infrared camera tracking system as the M56, but unlike
the M56 it lacks all of that weapon system’s self targeting and aiming
assist capability. Due to the high weight and lack of self-targeting, most
field units have begun replacing the M90 with the M56 “Smartgun” system.
The M90 can be hand carried and operated, but due to it’s high weight
it is most often seen mounted to the M48 or M56 combat harness and
weight distribution articulation arm system that makes the weapon easier
to use in the field. The M90’s onboard camera can be linked to the
standard Head Mounted Sight (HMS) for reliable point of aim sighting.
It can also be slaved with an optical cable to the M10 ballistic helmet
utilizing the drop down IR targeting eyepiece.
The entire gun assembly (with full 250 round ammunition load and the
M56 combat harness) weighs 27.2 kg.
The length of the weapon itself is 101 cm, and the length of the 3 barrels
are 58 cm.
OPERATING THE M90/A3
WARNING: This is a general description of operation procedures and
should not be used for instruction. Operators should refer to field manual
86-18-7 for further details of operation.
Prepping the M90/A3
The M90/A3 Vulcan Cannon system typically consists of four major components: the M48
or M56 combat harness; the head Mounted Sight (HMS); the Support Articulation Arm (SAA); and the weapon itself.
The M90 can be wielded free hand without the use of the combat
harness and SAA, but field operators are advised against this. The
weight of the weapon if operated by hand alone will eventually result
in lower back stress and Lower Back Trauma (LBT). For additional information
on LBT, see your Combat Medical services professional, publication
MED/M90 LBT 11-1-05.
To prep the M90 for combat, operators should first don the combat harness.
The M48 harness is constructed from composite micromesh ballistic armor
and is padded to ease chafing at the shoulders. The M56 combat harness
upgrade added additional padding at the shoulders and padding at the hips
as well. The armored breastplate of the M48 harness houses the PRC 489/1
communications receiver/transmitter. The M56 harness upgrade houses the
PRC 489/4 communications receiver/transmitter unit with wider bandwidth,
communication range and hard encryption to keep communication lines
secure. The M56 harness also houses the tracking and targeting processor
but this unit only acts as a targeting buffer for the HMS and does not aid
in targeting or target acquisition when used with the M90. Opening the
backplate in either the M48 or M56 armor gives access to the processor,
a sealed ‘black box’ line replacement unit (LRU) which can be easily unplugged
and replaced in the field should it fail.
The M48 MK3 or M56 MK3-A stabilized articulation/support arm is attached
to either the left or right hip mounting hardpoints (operators preference)
and plugged in via coaxial cable to the processor and power outlets in
the breastplate. The weapon itself is clipped and secured to the end of the
support arm. Regular routine maintenance of the arm assembly is suggested
to provide years of trouble free operation. The MK3 arm should have its
internal spring cable and wiring systems upgraded to the MK3-A standard.
Upgrades can be performed at any core system USCM armament facility.
The operator plugs the HMS into the universal tracking/targeting and
comms system in the armor.
Note: The M56 weapon assist tracker does not function with the M90 and
instead defaults to a basic hand operated targeting system. The weapon
tracker/targeting is jacked into the processor by a universal connector,
and the weapon itself must be powered up before the weapon is loaded.
The internally mounted DV5 Lithium battery unit supplies power for the
entire M90 weapon system.
The DV5 is good for up to 20,000 rounds when fully charged.
UPDATE 89-30-5: The DV5 batttery has been phased out of supply.
If the DV5 battery has failed on your M90, the DV9 Lithium battery unit,
good for up to 50,000 rounds when fully charged may replace it. The
DV9 may be run externally to the auxiliary power leads. Both ends
of the DV9 unit are plugged into the power leads that run from
the articulation arm to the weapon; common practice is to let the
battery hang free beneath the weapon where it is easily accessed
in an emergency.
“Yeah, the M56 is more expensive to produce and supply the troops
with, but what’s the alternative? The old M90 Minigun? Oh sure, the M90
can slice and dice and pound targets into fish food… but have you ever
used one free hand? The damn thing weighs a ton, shakes like an
Arcturian hooker on steroids and is guaranteed to kill you and everyone
around you… or ruin you for life.
I had 19 years in the Corps… and that last tour we were issued that
heavy piece of shit and thanks to the supply requisition morons we
weren’t issued a support vest rig. One damn tour and it ruined my back
and earned me a Section 4F medical retirement!”
- Retired Gunnery SGT. Jeremy “Fireball” Lewis, interview excerpt
from “Good Morning Gateway” segment on Military Spending.
M90 MOVEMENT:
While the operator is standing, the weapon is held and steered by it’s
under barrel foregrip and rear control grip. Operators have a wide degree
of motion with the weapon and can play it in an arc from their front to
their left sides, or point it directly upwards or down if firing from an
elevated position.
NOTE: Due to the high-speed rotating barrel mechanism it is inadvisable
for the operator to attempt firing the weapon from a prone position.
It is also inadvisable that the operators wear loose or ill fitting
clothing while operating the weapon. In wet environments, operators
should avoid using the M3 Rain Poncho and instead utilize the M3-P
Rain Parka. Serious injury or death could result if not followed.
See pamphlet M3-86-19-7 for additional information.
The articulation/stabilization arm is gyrostabilized and provides
additional recoil dampening to keep the weapon steady while the
operator is walking or running. The weapon has internal shock buffers
and recoil dampeners that allow the weapon to be operated free
hand if lacking the M48 or M56 support vest system. Shock buffers
should be replaced every 75,000 rounds by a licensed USCM technician.
FIRING THE M90:
All firing is controlled from the rear control handgrip. The right handed
pistol grip has five switches: a top mounted safety with flippable environment
cover, a front trigger for firing, a topside-mounted thumb activated
switch for Ammunition fusing selection, A side mounted thumb
switch for pre-spinning the barrel rotation and a bottom button to
allow select firing between Burst and Autofire modes.
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Clicking off the safety will automatically charge the weapon. (If
there is a round already in the breech, the weapon’s diagnostics
will prevent any further loading.) The Burst setting will fire a
three round burst per trigger pull while the Autofire setting will
continue to fire the weapon at it’s full cyclic rate as long
as the trigger remains depressed. Left hand control grip replacements
are available if required.
Contact your supply requisition officer for additional information.
The standard issue ammunition for the M90 is the M245 10mm x 28
HEAP (High Explosive Armor Piercing) round which is a 350 grain
caseless projectile encased in a rectangular block of nitramine.
Considerably higher powered than the M309 round used in the Pulse
Rifle, it is most often used against fixed emplacements and armored
vehicles although it can also be used against enemy personnel.
The Geneva Colony Convention of 2162 has suggested that HEAP
rounds no longer be used against personnel citing it as being
“inhumane,” but an official ruling has not as of yet been issued.
USCM personnel are authorized to use HEAP rounds at their own
discretion. M245 ammunition is stored on a block continuous plastic
non-disintegrating snake drive link belt in the box magazine,
which can be reloaded in the field. The self-powered snake drive
motor in the box magazine drives the feed mechanism through a
side mounted feed chute and into the breech at the top of the weapon.
In the event of a stoppage, the barrel rotation interlink mechanism
can be disengaged and the barrel assembly counter-rotated,
ejecting the round and clearing the breech. The barrel assembly can
be manually rotated one turn per barrel to manually charge the
system. In the event of a complete electrical failure, the system
can be manually fired by hand rotating the barrel with the grip
safety lever deactivated and the trigger engaged. This will allow
single round firing in an emergency situation. In the event of an
electrical failure, please take the weapon to an authorized USCM
armorer for immediate service.
The M250 10mm x 28 ammunition is a 230 grain caseless projectile
encased in a rectangular block of nitramine. Unlike the M245 HEAP
round, the M250 differs in having a user selectable fuse setting.
The switch on the top of the hand grip next to the safety is used
to select the ammunition fusing, which is set electronically as each
round is loaded into the chamber. The ‘Super’ setting is optimized
against soft targets and will detonate the round on impact, while
the ‘Delay’ setting explodes the shell only after penetrating the
target armor.
Unlike the near instantaneous switch activation of the M56 Smart
Gun system, ammunition fusing with the M90 and M90A2 can take
up to fifteen seconds to cycle due to the older technology of the
M90 system. It is recommended that ammunition fusing changes
be done in a non-hostile environment to reduce the chance of
injury to the operator in the field. The later production model
M90A3 has a revised hardware system and ammunition fusing
selections can be performed in as little as seven seconds.
