Matador MAT-9 | TRIAD Bullpup Chassis

Bring a compact bullpup layout to your Matador Arms MAT-9 with the A3 Industries TRIAD Modular Bullpup Chassis. The TRIAD houses a standard mil-spec AR lower receiver and pairs it with a bufferless upper, giving you the versatility of the AR platform in a bullpup package. This complete kit includes the TRIAD chassis and the installation kit made specifically for the MAT-9, along with a barrel extension and handguard extension.

Why a bullpup?

A bullpup shortens your firearm's overall length without shortening the barrel, making it far more maneuverable in tight spaces. Moving the bolt and barrel rearward also shifts the center of mass behind your grip, for better balance and control, and the shorter distance between the action and butt plate sends recoil more directly into your shoulder with less muzzle rise.

A better bullpup trigger

The TRIAD is designed to avoid the typical "bullpup trigger" feel. Instead of a sliding trigger bar, it uses a traditional pivoting front trigger and a bell crank that converts the pull of the front trigger into a push on the rear trigger. The result is a natural-feeling trigger with a short, rigid rear linkage that weighs just 0.8 oz. Oil-embedded bronze bushings and ±0.001" tolerances at every pivot point provide smooth, virtually frictionless movement. A light linkage return spring adds about one pound to your trigger's pull weight.

Pistol or rifle configuration

• Rifle: includes a standard compact butt plate and a 1.5" extended butt plate, a cheek rest, and two steel QD sockets.
• Pistol: includes a featureless receiver end cap with no cheek rest and a rear-facing sling socket (three QD sockets total), designed to prevent shouldering. If you later register your firearm as an SBR, a butt plate upgrade kit is available.

Matador Arms MAT-9 compatibility

The TRIAD has been tested and approved with the MAT-9 9mm upper, which has a 7.825" barrel. Running the MAT-9 requires a 9mm magwell conversion insert in your lower for Glock or Colt magazines, or a Mean Arms EndoMag.

What's included

• TRIAD chassis body with front trigger housing assembly (front trigger and selector installed, adjusted, and tested)
• Matador Arms MAT-9 installation kit
• Barrel extension
• Handguard extension
• All internal and assembly components (no AR lower parts kit needed)
• Assembly wrenches and instructions
  

Additional components required

• Matador Arms MAT-9 upper receiver
• Standard forged mil-spec AR lower receiver
• 9mm magwell insert (Glock or Colt magazines) or Mean Arms EndoMag
• AR bolt catch with spring, pin, and plunger
• Single-stage, flat-faced AR trigger
• 3/8" drive ratchet for assembly

Lower receiver compatibility

The TRIAD requires a standard forged mil-spec AR lower receiver. Billet lowers and lowers with integrated trigger guards are not compatible. Verified compatible lowers include PSA, Colt, Anderson, Aero Precision (without integrated trigger guard), and Spikes Tactical (without integrated trigger guard).

Trigger compatibility

Any single-stage trigger with a flat (not curved) face should work. We recommend a short-reset cassette trigger for best performance. CMC and Radian Vertex triggers are not compatible due to their size.

Assembly

Assembly is straightforward and takes about 30 minutes. Remove the left chassis half, install your lower with the trigger and bolt catch already in place, reinstall the chassis half, and adjust the trigger actuator. Then install the end cap or butt plate and mount the M-LOK front takedown lug on your upper.

Construction and included components

• 6061 aluminum front trigger housing
• 7075 aluminum front trigger
• Three 4140 steel anti-walk trigger pins
• A3 ambidextrous selector with detent and spring
• QPQ-coated 17-4 stainless steel front trigger linkage
• 7075 aluminum transfer bar and rear linkage with 841 oil-embedded bronze bushings
• Acetal (Delrin) guide and trigger actuator
• Injection-molded, 30% glass-reinforced Zytel main chassis housing
• 4140 steel and 7075 aluminum threaded chassis inserts
• 4140 steel QD sockets: two on rifle configurations, three on pistol configurations
• 4140 steel magazine release
• 7075 aluminum extended right-side magazine release button and left-side lever
• Three 4140 steel ball-detent takedown pins
• A3 Xeno-patterned, reduced-angle polymer grip

Legal compliance

With its 7.825" barrel, the MAT-9 must be built in pistol configuration, or registered as a short-barreled rifle (SBR) with the ATF before being assembled in rifle configuration. You are responsible for ensuring your configuration complies with all federal, state, and local laws, including the National Firearms Act (NFA) and Gun Control Act (GCA).

The TRIAD is a chassis, not a lower receiver. It is an unregulated accessory and ships directly to your door with no FFL transfer required.

Important: Review the TRIAD Info FAQ before ordering for full configuration details, compatibility requirements, and specifications.