The SIG SAUER MCX-SPEAR LT IR combines the compact, bufferless MCX operating system with a 9-inch 300 Blackout barrel and SIG's Gen II near-infrared-reducing FDE Cerakote. Cataloged by SIG SAUER as a factory pistol, model PMCX-300B-9B-IR includes a folding SIG Pivoting Contour Brace, adjustable gas-piston operating system, fully ambidextrous controls and a SIG QD suppressor-ready flash hider.
The result is a compact large-format pistol configured around the characteristics that make 300 BLK useful in short-barreled platforms: dependable piston operation, a fast 1:5 barrel twist, a common 5/8-24 muzzle thread and the ability to tune the gas system for changing ammunition and suppressed-use conditions.
Gen II NiR FDE Cerakote
This MCX-SPEAR LT wears SIG's Gen II NiR FDE Cerakote. NiR refers to near-infrared signature-reduction properties intended to reduce the finish's visibility under compatible night-observation equipment while also providing the wear and corrosion resistance associated with a ceramic firearm coating.
The coating is a signature-management feature, not an electronic night-vision or thermal device, and it does not make the firearm invisible. Apparent performance can vary with the observation system, illumination source, distance, environment, background and surface condition.
Purpose-Built 9-Inch 300 Blackout Barrel
The 9-inch cold-hammer-forged carbon-steel barrel uses a fast 1:5 twist to stabilize the broad range of projectile weights commonly offered in 300 BLK ammunition. The barrel is threaded 5/8-24 and arrives with a Rocksett-applied SIG QD suppressor-ready flash hider.
The 9-inch configuration offers additional barrel length and ballistic potential compared with the most abbreviated personal-defense MCX models while remaining highly compact when its brace is folded.
Adjustable Short-Stroke Gas-Piston System
Unlike a conventional direct-impingement AR-pattern firearm, the MCX-SPEAR LT operates through a piston system contained within the upper assembly. It does not require a traditional AR buffer tube extending behind the receiver, allowing the brace to fold alongside the firearm without disabling the core action architecture.
An adjustable gas system gives the operator a way to accommodate differing ammunition and operating conditions. Any adjustment should follow SIG SAUER's current manual, and the firearm should be function-tested with the exact ammunition and suppressor configuration intended for use.
Suppressor-Ready Configuration
SIG equips this pistol with a SIG QD suppressor-ready flash hider. The muzzle device is installed with Rocksett, a high-temperature thread-locking compound commonly used on suppressor mounts.
“Suppressor-ready” describes the muzzle configuration; it does not mean a suppressor is included. Confirm that any suppressor and mounting system are expressly compatible with the installed muzzle device, barrel thread, caliber and ammunition. Suppressors are separately regulated under federal law and may also be restricted by state or local law.
Folding SIG Pivoting Contour Brace
The factory-installed SIG Pivoting Contour Brace folds to the side, reducing the pistol's published length from approximately 27.5 inches to 19.3 inches. The folding arrangement is particularly useful for compact storage and transport while retaining a conventional rear attachment point when deployed.
This model is manufactured and identified by SIG SAUER as a pistol. It is not the stocked MCX Rattler LT short-barreled rifle. Owners should not install a shoulder stock or otherwise change the factory configuration without first confirming the firearm's resulting classification under all applicable laws.
Fully Ambidextrous MCX Controls
The MCX-SPEAR LT is designed around fully ambidextrous operating controls, supporting right- or left-handed manipulation without requiring an aftermarket control conversion. A forward assist is also included.
SIG's Flat Blade Match Trigger provides a flat trigger face and a familiar straight-line interface for shooters who prefer that geometry over a traditional curved trigger.
Lightweight M-LOK Handguard
A lightweight alloy handguard provides M-LOK accessory-mounting positions while protecting the barrel and piston system. The upper receiver supplies the mounting surface for a user-selected optic. Because SIG does not list iron sights or an optic among the included components for this SKU, plan to add an appropriate sighting system before live-fire use.
Keep lights, aiming devices and other accessories clear of the gas-regulator area, muzzle device and suppressor interfaces. After mounting an optic or laser, verify all fasteners and confirm zero before relying on the equipment.
Interchangeable MCX Architecture
The MCX-SPEAR LT family is designed around an interchangeable-barrel architecture. That flexibility does not make every MCX component universally interchangeable. Barrel assemblies, bolts, handguards, gas components, muzzle devices and ammunition must be matched to the applicable MCX generation and configuration.
Conversions and major component changes should follow current SIG SAUER instructions and, when appropriate, be completed or inspected by a qualified armorer or gunsmith. Always verify caliber markings, headspace, gas configuration and bore clearance before firing a modified firearm.
MCX-SPEAR LT IR Pistol Versus MCX Rattler LT SBR
The MCX-SPEAR LT IR pistol and the MCX Rattler LT 6.75-inch SBR share SIG's compact piston-driven MCX foundation, but they are configured for different priorities.
- MCX-SPEAR LT IR pistol: 9-inch 300 BLK barrel, folding PCB, 19.3-inch folded length, 5.6-pound published weight and Gen II NiR FDE Cerakote.
- MCX Rattler LT SBR: shorter 6.75-inch barrel and a factory shoulder stock in an NFA-regulated short-barreled-rifle configuration.
The SPEAR LT IR provides more barrel length, an IR-signature-conscious finish and factory pistol classification. The Rattler LT SBR prioritizes minimum size and a shoulder-stock configuration, but requires the separate federal and local procedures applicable to an NFA firearm.
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