Small arm designs are introduced in both revolutionary and evolutionary processes, each being equally important to developing a reliable and capable firearm system. For manufacturers, engineering a new gun and its progressive iterations, is a painstaking progression that requires refinement, numerous evaluation cycles, and performance improvements. For the consumer, the excitement of a new system is intertwined with compatibility concerns, the hope for additional features in future releases, and waiting  – a cycle that is not unique to the firearm industry. In early 2015, SIG Sauer released the MCX, a revolutionary design in a market awash in direct impingement AR-15 variants. In the years since the initial release, the MCX progressed into the MCX Virtus, arriving at where we are today – the introduction of the SIG MCX SPEAR-LT.

Below: The SPEAR-LT with the SIG SLX556-QD suppressor.

The MCX SPEAR-LT may not seem overly impressive at first glance, but it is the most advanced update to date, adding features, reducing weight, while remaining completely backwards compatible with all of the MCX Virtus models over the past five years.

SIG MCX @ TFB:

• SILENCER SATURDAY #226: The MCX Virtus Piston System
• Commercially Available! The SIG Sauer NGSW MCX-SPEAR
• [TFB GUNFEST] The SIG Sauer MCX Spear NGSW Rifle
• Ultimate Guide: The SIG Sauer MCX Rifle, Carbine And Pistol Platform

Today’s gear list:

• Rifle: SIG Sauer MCX SPEAR-LT 5.56, 16″, RMCX-556N-16B-LT (New; this article topic)
• Rifle: SIG Sauer MCX Virtus 300BLK, 9″, PMCX-300B-9B-TAP
• Optic: SIG Tango 6 1-6X
• Optic: SIG Romeo 8H
• Suppressor: SIG Sauer SLX556-QD
• Suppressor: SIG Sauer SLX762-QD

Compare and Contrast: The new MCX SPEAR-LT 16” 5.56 carbine (top) and the MCX Virtus 9” 300BLK (bottom).

TFB FIRST LOOK: Introducing the New 5.56 SIG MCX SPEAR-LT

Alone, a short stroke piston is not exactly a ‘revolutionary design’ – several rifles and carbines have used this system with great success. But SIG refined a series of features around the short stroke piston to develop an advanced rifle that addresses many of the shortcomings displayed in the AR-15 and other weapon systems.

If you own an MCX Virtus, don’t worry. All of the parts are backwards compatible. But for obvious reasons you may not be able to take advantage of all of the new features of the MCX SPEAR-LT should you decide to mix and match.

The hand guard on the SPEAR-LT is slimmer, lighter, and is securely fastened to the upper receiver with two bolts. Some users were concerned with the possibility of a shift in the point of impact (POI) when using laser devices that were attached to the hand guard on the Virtus systems. Although I tested this several times and my IR laser held a zero even after being completely removed. The lower profile of the SPEAR-LT hand guard does allow for a more secure supporting hand grip.

Using a pushbutton design rather than a pull up and rotate action, the new MCX collapsing stock folds easily out of the way when needed. There is a removable cheek rest for those shooters who don’t like the feel of cold metal on their sensitive skin.

Features:

• 13” Lightweight Ergonomic Handguard
• SIG Flatblade Match Trigger
• Fully Ambidextrous Controls
• Interchangeable Barrels
• Push-Button Folding Stock With Cheekrest
• SIG QD Suppressor-Ready Flash Hider

Specifications:

• SKU: RMCX-556N-16B-LT
• MAP Pricing: As low as $2499
• Caliber: 5.56 NATO
• Frame Material: Aluminum
• Frame Finish: Coyote Anodized
• Barrel Material: Cold Hammer Forged Carbon Steel
• Barrel Finish: Nitride
• Magazine Capacity: 30 Rounds
• Sights: Optics Ready
• Trigger: Flat Blade Match
• Measurements:
  • Overall Length: 34.3 in / 870mm
  • Overall Height: 7.8 in / 197mm
  • Overall Width: 2.8 in / 71mm
  • Barrel Length: 16 in / 406.4mm
  • Barrel Twist: 1:7 in / 1:177.8mm
  • Weight W/Magazine: 7.4 lb / 3.4 kg

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Fully Ambidextrous

One of the biggest additions to the MCX SPEAR-LT is the right side bolt release, making this rifle completely ambidextrous. This minimalist design was first introduced with the SIG Switchblade M400 AR-15 series and it is both low profile and easy to use. It looks dainty, but it’s not – it is solid and it works.

Here’s a closer look at the new pushbutton collapsing stock system – just push down and rotate the stock clockwise.

Below is the left side bolt that secures the hand guard to the upper receiver. To remove the hand guard, unscrew the two bolts, remove the pivot takedown pin, and pull forward.

Besides the ambidextrous right side bolt release, there are some internal geometry changes in the MCX SPEAR-LT lower receiver (top) compared to the MCX Virtus lower receiver (bottom). If you are mocking my dirty MCX Virtus lower, be advised that the MCX is my favorite carbine and it gets shot a lot.

A side profile look at the SPEAR-LT (top) and the Virtus (bottom) lower receivers notes that the right side bolt release is really the only difference between the two. Also note that the whole rifle is anodized in coyote FDE whereas the MCX Virtus could have both anodized and Cerakote coated parts from the factory.

The recoil springs and bolt carrier groups have the same external geometry, which allows everything to remain backwards compatible.

But one of the new features of the SPEAR-LT is the ability to use any MILSPEC AR-15 trigger. This change requires a redesign in the MCX firing pin lock system. The SPEAR-LT BCG (top) appears to have the firing pin lock on the left side of the bolt directly behind the firing pin (pictured here on the bottom of the firing pin). Where as the Virtus firing pin lock comes down from the top.

Below: The firing pin lock design (highlighted in yellow) on the MCX Virtus from the MCX Small Parts Shopper (SIG). We will do a full field strip in the coming weeks – I want to get a good number of rounds through this gun as it came from the factory before I do any disassembly.

After a cursory review of both the SPEAR-LT (top) and the Virtus (bottom) upper receiver groups, I wasn’t able to detect any significant differences.

At first I bemoaned the 16 inch barrel as the first SPEAR-LT release (yes, I use terms like ‘bemoaned’ and complain about the brand new first production MCX SPEAR-LT as being ‘too long’). But the barrel length does make perfect sense. With pistol stabilizing braces firmly in the crosshairs of ATF regulations and the NFA application process for making or transferring a short barrel rifle (SBR) taking months to complete, a 16″ rifle is the best way to get the SPEAR-LT in as many hands as possible as quickly as possible.

Besides, when barrels and hand guards become available, new owners can start the ATF Form 1 process and created their own SBR while still shooting their 16″ gun. MCX barrel swaps can be completed with simple tools, don’t require an armorer like AR-15 barrel changes, and can be completed in as little as two minutes. As a reminder, always read the user manual before operating or disassembling a new firearm to ensure the proper procedures are being followed.

Below: The 9″ MCX Virtus in 300BLK suppressed with the SIG SLX762-QD (top) is about the same length as the unsuppressed 16″ SPEAR-LT in 5.56 (bottom).

As a huge fan of the SIG MCX Virtus, I am extremely pleased to finally witness the evolution of the MCX SPEAR-LT. This rifle drops some weight, adds new features, remains backward compatible, and improves on an already impressive system that is used by military, law enforcement, and civilians around the world. Most importantly, the MCX SPEAR-LT is in production and is available for purchase starting tomorrow.