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SA-12 Viper

This page is a work in progress by its author and should not be considered final.

SA-12 Viper

SA-12/89 Viper Combat Shotgun w/ folding stock & shell carrier


Automatic shotgun

Place of origin

Etoile Arcture

Service history

In service

2005 - present

Used by

See Users

Production history


Sequoia Weaponworks




Sequoia Weaponworks

Unit cost


Number built

Heaps and many


SA-12/76 Tactical Shotgun
SA-12/89 Combat Shotgun



2.79-2.85 kg empty,
3.76-3.82 kg loaded


1052 mm w/ fixed stock
1047 mm w/ stock extended
886 mm w/ stock folded

Barrel length

470 mm (18½ in) or
508 mm (20 in)


12 Gauge Magnum


gas operated,
double action

Rate of fire

20 rounds/min

Muzzle velocity

420 m/s for buckshot
600 m/s for sabot slugs
472 m/s for solid slugs
384 m/s for breeching slugs
286 m/s for Ferret barricade

Effective firing range

20 m w/ buckshot
40 m w/ slug
125 m w/ sabot slug

Maximum firing range

125 m

Feed system

6- or 8-round
overbarrel tubular


ghost ring or
rear aperture,
hooded post

The SA-12 "Viper" is a dual-action, selective autoloading and manual pump action, magazine fed, semi-automatic tactical shotgun with a low bore axis, having a horizontal upper tubular magazine and top-loading port with lower barrel and bottom shell ejection. The SA-12 has been designed as a military and law enforcement weapon with ambidextrous handling and low maintenance attributes. It combines the low recoil characteristics of a gas operated weapon with a low bore axis for improved accuracy and a top loading port for faster combat loading. The gas operating system delivers a soft recoil allowing the SA-12 to be fired as accurately from the shoulder, hip or with one hand.
In normal operation a self regulated gas system is used to cycle the weapon which is self cleaning and able to handle any high impulse or hot load by automatically compensating for differing sized cartridges and power levels. For lower power rounds the option is provided of shutting off the gas system. This converts the weapon to a manual repeater allowing firing of low velocity ammunition lacking the recoil energy to cycle the automatic mechanism. Thus, the SA-12 can be used for a number of missions including riot control, close quarters combat, door breaching and personal protection.


The receiver is milled as a single piece from lightweight solid billet Ergal 55 (aluminium alloy with steel-like mechanical performance) having a sand blasted Type III hard anondized matt black finish. The bolt, carrier, gas system and barrel are made from AISA 410 stainless steel with a Type M manganese phosphate corrosion resistant finish. The bore, chamber and gas system are all chrome plated for increased reliability and corrosion resistance, and the bolt and elevator have a physical vapour deposition (PVD) titanium nitride protective non-glare coating. The barrel has a tapered profile and incorporates an internal screw-in choke system with the options of a cylinder bore (fitted as standard) to a full choke for optimising shot strings and patterning. Above the barrel is an eight or five-shot tubular magazine with a shell follower surrounded by a synthetic handguard (or optional handguard with mounting for a tactical flashlight, multifunction illuminator or laser aiming module). The grip has an extended slide for improved control and in manual mode is pumped forward to cycle the action (which is reversed in the upper magazine configuration).
All furniture, including the slide, are made from Zytel Super Tough glass-filled polymers. There is a choice of two stock options: a one piece pistol grip straight line stock designed to distribute recoil forces evenly across the butt recoil pad and the palm of the shooting (strong) hand; and a top-folding skeletonized stock of stamped steel construction that can dramatically shorten the length of the weapon for manoeuvring in close environments. The folding stock lays across the receiver with clearance for the rear sight when folded, and can fold/unfold instantly at the push of a quick release button. An aftermarket elastomeric polymer five-shell carrier can also be fitted beneath this stock as a speed loader.
The receiver is drilled and tapped for dovetail mounts. The Combat shotgun has a rear open notch and flip-up ghost ring (diopter) front sight for both eyes open aiming, and a protected fixed front post sight on the barrel that also works with the rear notch when the ghost ring is folded. Both sights have Tritium luminous dots for night shooting and are adjustable for windage and elevation. A Weaver-style accessory rail can also be attached to the receiver ahead of the loading port for mounting aftermarket optical and night vision sights. The Tactical shotgun differs by mounting a carry handle in place of the dovetail mount, this being offset to the left of the the receiver and high enough not to interfered with the receiver top loading port. The handle is grooved containing a sliding-type tangent-leaf rear sighting unit and the front sight is a high mounted hooded post.

Operating principles

The gas operating system is self-regulating having gas exit ports spaced concentrically around the barrel that operate a piston which actuates a connecting rod and recoil spring assembly. On firing these move rearwardly to cycle the next shell into the chamber from a shell space in the carrier above the breech. The bolt assembly has both upper and lower bolt members, with locking lugs on the opposite sides of the lower bolt being released by rearward movement of the upper bolt member. Reciprocal guide pins are located in the lower bolt member and are retracted into the face of the lower bolt to allow a spent shell to be ejected through the ejection port. The impact of the lower bolt member at the rear of the receiver drive the pins forwardly to direct a new shell into the breech. The barrel has extensions to stop the front of the shell from passing through and out the bottom ejection port upon loading and to guide and help deliver the shell into the barrel chamber.
The SA-12 shotgun is loaded via a top loading port on the receiver which is protected by dividing spring-loaded dirt/dust covers. In combat this allows rapid loading into the shell carrier without having to lower the muzzle or taking eyes off a target. This is accomplished by holding the weapon level by its grip and the stock trapped beneath the arm and charging the magazine using the free hand. This immediate action drill can be used to replace rounds during combat and be performed by touch only allowing the operator to continue scanning the environment for potential threats. The spent cases eject through a port on the bottom of the receiver minimising visual signature when firing.
The modular trigger assembly has a hammer which is rotated rearwardly by the lower bolt and which returns to a "short lock time" position held ready to fire by a sear. The firing pin is driven through a bore in the lower bolt by the hammer. A firing pin block prevents premature automatic firing of a subsequent shell before the locking lugs on the lower bolt are substantially engaged. A crossbolt push-button safety is located in front of the trigger in the trigger guard which when pushed locks the trigger, sear and hammer simultaneously to prevent accidental firing if the weapon is dropped or jolted.
Operators can easily switch between action styles via a rotary ring toggle switch located ahead of the slide. This consists a semi-automatic mechanism for high impulse loads (buckshot, slugs, flechettes, etc); and a manual pump action mode that unlocks the slide for cycling low velocity ammunition lacking the recoil energy to cycle the gas system (CS ferret, bean bag, Hatton rounds, flares, etc). An operator may also chamber a high or low-impulse round manually and fire it without switching between either modes for fast employment. To handle the widest variety of lethal and less-lethal ammunition, including 70, 76 and 89 mm cartridge lengths and plastic and brass-cased shotshells, the SA-12/89 is provided with an 89 mm (3½ in) chamber while the SA-12/76 has a corresponding 76 mm (3 in) chamber.


SA-12/76 Viper Tactical Shotgun

    Law enforcement model chambered in 12 gauge x 3" shotshells with a six round magazine.

SA-12/89 Viper Combat Shotgun

    Military model chambered in 12 gauge x 3½" shotshells with an eight round magazine.


Etoile Arcture

  • Etoile Arcture Special Forces

  • Etoile Arcture Gendarmerie Force

  • Police Service of Etoile Arcture


  • Forces Spéciales

  • Corps des Marine

  • Service Gendarmerie

  • Sécurité intérieure

Monavian Empire

  • Monavian Royal Marine Corps

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  • Cartridge: 18.5×76 mm (12 gauge × 3") or 18.5×89 mm (12 gauge × 3½") rimmed shotshells

  • Action: gas operated, double action

  • Locking: rotary bolt w/ 4 lugs

  • Weight: 2.85 kg empty, 3.82 kg loaded (Combat), 2.79 kg empty, 3.76 kg loaded (Tactical)

  • Overall length: 1052 mm w/ fixed stock, 1047 mm w/ stock extended, 886 mm w/ stock folded

  • Barrel length: 508 mm (20 in) (Combat), 470 mm (18½ in) (Tactical)

  • Muzzle device: door breach/glass breaker

  • Feed type: 6 round 3" shotshell overbarrel tubular magazine or 8 round 3½" shotshell overbarrel tubular magazine + 1 in the chamber

    • #OO buckshot

    • Foster-type rifled slug

    • Hatton door breaching round (compressed zinc)

    • Ferret barricade penetrating round (non-pyrotechnic irritant agent liquid or powder CN, CS, OC and inert fillers)

    • stingball (.32 cal rubber balls)

    • Rocket rubber baton round (fin stabilised 80 durometer rubber projectile)

    • bean bag

    • hydro-kinetic impact bag

  • Sights: ghost ring rear aperture and hooded post foresight (Combat), tangent-leaf rear and hooded post foresight (Tactical)

  • Muzzle velocity:

    • 420 m/s for buckshot

    • 600 m/s for sabot slugs

    • 472 m/s for solid slugs

    • 384 m/s for breeching slugs

    • 286 m/s for Ferret barricade

    • 99 m/s for stingball, bean bag

  • Effective range:

    • 20 m w/ #OO buck

    • 40 m w/ stingball (improved cylinder choked)

    • 25 m w/ bean bag (improved cylinder choked)

    • 25 m w/ Hatton round (improved cylinder choked)

    • 40 m w/ Rocket rubber baton round

    • 75 m w/ rubber slug

    • 125 m w/ Foster-type rifled slug (improved cylinder choked)

  • Fire control: push button crossbolt sear block

  • Rate of fire: 60-75 rpm practical, 240 rpm cyclic

  • Trigger pull: two-stage Match, non-adjustable 24.5 N + 32.25 N

  • Unit replacement cost: US$1,850