by Max Barry

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by The Unitary Technocracy of Etoile Arcture. . 126 reads.

MAG12 MK 4 Assault Shotgun

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

MAG12 MK 4 Assault Shotgun


Automatic shotgun

Place of origin

Etoile Arcture

Service history

In service

2015 - present

Used by

Etoile Arcture
Special Forces

Zinairian Army
Forces Spéciales

Production history


Sequoia Weaponworks




Sequoia Weaponworks

Unit cost


Number built

Heaps and many


See below



5.3 kg


960 mm

Barrel length

451 mm


12 Gauge magnum


gas operated,
piston driven,
long stroke

Rate of fire

250 rounds/min

Muzzle velocity

? m/s

Effective firing range

50 m

Maximum firing range

200 m

Feed system

10-round detachable
box magazine or
20-round drum



The MAG12 MK 4 Assault Shotgun, also know as the "Punisher", is a lightweight, air cooled, long-stroke gas piston operated, magazine fed, smoothbore, internally choked, selective fire semi-automatic (i.e. self-loading) shotgun chambered for 12 gauge ammunition. It shares the same ergonomics, controls and manual of arms with ambidextrous safety and mag release as the G500 Modular Weapon System (G500 MWS) for easy familiarity and training conversion. The MAG12 is configured inline with a long-stroke straight line recoil path and high effect muzzle brake that reduce muzzle climb, peak recoil and cyclic rate of fire for high controllability in semi-auto fire. A self-adjusting gas system vents excess gas for recoil mitigation/attenuation and alleviation of stress on the operating components for increased reliability.
The MK 4 "Punisher" is designed to fire high-impulse, multiple projectiles with an effective range of 40-150 metres during close quarters battle, door breaching, riot control and bunker defence. Recommended ammunition loads include standard or shaped-pattern shot rounds fired from choked barrels, fin-stabilized flechettes, solid and sabot slugs, and specialized FRAG-12 and flare rounds available in various colours. The self-adjusting gas system can also cycle low power ammunition, including beanbag, stingball, rubber batons/slugs, Hatton door breaching and Ferret barricade penetrating chemical rounds. The barrel has an internal choke system with replaceable screw-in choke tubes for greater accuracy and tighter shot patterns, and muzzle threads for tactical stand-off devices.


The MAG12 has an aluminium reinforced GF/PA-6 glass fibre/polyamide-6 upper receiver and handguard, and single moulded polyamide lower receiver, magazine well and pistol grip partially resembling the G500 MWS. Controls consist of an ambidextrous safety lever, magazine release and bolt carrier group release on the lower reciever, and a non-reciprocating forward charging handle with oversized tactical bolt handle on the left side of the upper receiver. A larger ejection opening and cut-out on the right side of the receiver is protected by a spring-loaded cover to prevent penetration of dust and foreign particles into the receiver that can foul the action. The fore-end is ventilated and features moulded-in four-quadrant polylithic accessory rails combining a Vltor KeyMod Universal Mounting System in the 3 and 9 O'clock positions and MIL-STD-1913 Picatinny rails in the 6 and 12 O'clock positions. A carry handle with open sights or any aftermarket iron sights or optics can be installed on the top rail, which has a 20 MOA elevation cant. The buttstock is an aluminium LR300-style side-folding telescoping skeletonized design with a five-position collapsible mechanism and non-slip polymer buttpad.
The gas system is constructed from 4140 chromium molybdenum alloy steel (aka ordnance steel), consisting of the bolt group, chamber, barrel bore, piston and gas cylinder, that are chrome lined for gas erosion and corrosion resistance and finished with a matt black manganese phosphate coating for durability. The barrel has a cylinder bore (no-choke, full-open bore) and accepts interchangeable screw-in internal choke tubes e.g. cylinder bore (5 notches) as standard for using frangible compressed zinc breaching slugs in dynamic entries to remove door hinges and door locks; improved cylinder bore (4 notches) that increases hit probability with rifled slugs and produces tighter patterns with a wide range of loads (shot, bean bag, etc); modified (3 notches) for tight shot pattern density; and full (1 notch) for long range shooting with sabot slugs. External threads on the barrel over the choke area accept stand-off muzzle devices such as a door breach/glass breaker device.

Operating principles

The fast cycling self-adjustable gas system is patterned on a conventional closed-bolt operating system with a gas chamber and piston, comprising a long-stroke gas piston located above the barrel and a rotary bolt locking mechanism in the upper receiver. The weapon is cycled by gas diverted by gas ports in the barrel bore to a gas cylinder that impinges upon a annular gas piston to drive the bolt carrier rearwardly along dual guide rods machined into the receiver. The self regulating gas system automatically adjusts to the recoil of the weapon (aka infinite adjustments) allowing cycling of all types of 12 gauge shotshells, loads and powder charges.
The breach is locked and unlocked by a substantial "monolithic" 12 gauge bolt carrier with a heavier reciprocating mass, featuring a rotating bolt with two massive locking lugs in the bolt head that engage with corresponding recesses in the barrel extension. A cam pin rides an S-shaped cam track on the bolt to control the locking and unlocking of the chamber. A spring extractor is located on the bolt head, and as the bolt travels back it engages with the rim of a shotshell to extract and eject a spent case until reaching a stop, leaving the weapon cocked and ready to fire, before the long-stroke recoil spring, comprising a telescoping piston rod that compresses "Belleville" conical spring washers, forces the bolt forward again where it will strip a fresh round from the magazine to load in the chamber. A bolt hold-open device locks the bolt to the rear when the mag is empty or whenever the bolt is manually pulled back without a magazine loaded, allowing faster reloads and clearing of the chamber of misfired or dud rounds.
The magazine well is slanted at 45° compared to the straight geometry of the G500 magwell allowing it to accommodate AK-pattern curved magaines, with the push-button release mechanism of the G500 being replaced by a spring-loaded plunger to ensure smooth and fast mag changes. The weapon can accept all types of 12 gauage ammunition and functions with both 70 mm (2¾") and 76 mm (3") length rimmed shotshells. Sequoia Weaponworks provide a 10 round single stack curved polymer magazine modelled on an extended length 7.62 mm AK-pattern detachable box magazine, with an optimised feed geometry that reliably feeds ammunition of both lengths loaded into the same magazine. Constructed from Zytel impact-resistant thermoplastic polyamide reinforced by steel mesh at the feed lips, the magazine also features a robust polymer four-way self-leveling/anti-tilt follower and strengthened heat-treated chrome silicon wire spring for reliable operation. The weapon can also use magazines compatible with OEM (original equipment manufacturer) AK-pattern mags made for the SAIGA-12/VEPR-12 shotguns and a select few aftermarket mags including the MD Arms MD-20 20-round drum magazine and Izmash 10-round box mag.


MAG12 MK 4 Assault Shotgun

    Standard version chambered in 12 Gauge rimmed shotshells.


Etoile Arcture

  • Etoile Arcture Special Forces


  • Zinarian Army


  • Forces Spéciales

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  • Cartridge: 18.5×70 mm (12 gauge × 2¾") or 18.5×76 mm (12 gauge × 3") rimmed shotshells

  • Action: gas operated, piston driven, long stroke

  • Locking: rotary bolt w/ 2 lugs

  • Weight: 3.5 kg empty, 5.3 kg loaded (20 rds)

  • Overall length: 960 mm w/ stock extended, 886 mm w/ stock folded

  • Barrel length: 451 mm (17¾ in)

  • Muzzle device: door breach/glass breaker

  • Feed type: 10 round single stack 3" shotshell detachable box magazine or 20 round 2¾" shotshell detachable drum magazine

    • #OO buckshot

    • flechette (19 × MIL-F-8167 8 gr flechettes)

    • Foster-type rifled slug

    • FRAG-12 (HE, HE-FA, HE-AP)

    • Hatton door breaching round (compressed zinc)

    • armour piercing

    • illum

    • 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: aftermarket iron sights, day optics, etc

  • Muzzle velocity: ? m/s

  • Effective range:

    • 25 m w/ #OO buck

    • 50 m w/ stingball (improved cylinder choked)

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

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

    • 40 m w/ Rocket rubber baton round

    • 45 m w/ flechette

    • 75 m w/ rubber slug

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

    • 200 m w/ FRAG-12

  • Fire control: drop-in replaceable trigger group, ambidextrous selector levers

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

  • Trigger pull: single-stage Match, non-adjustable 17.7 N pull

  • Unit replacement cost: US$2,500