Sig Sauer MCX Spear LT 5.56 NATO
Model: RMCX-556N-16B-LT-B
Sig Sauer MCX Spear LT 5.56 NATO
Model: RMCX-556N-16B-LT-B
Full Specifications
About This Firearm
The MCX Spear LT is Sig Sauer's lighter derivative of the MCX platform, which itself traces back to the U.S. Army's Next Generation Squad Weapon program. Unlike conventional AR-15 rifles, it runs a short-stroke gas piston system with no buffer tube, allowing the polymer stock to fold flat against the receiver. That folding stock brings the stored length down dramatically from the 34.3-inch overall measurement.
The 16-inch cold hammer-forged barrel sits in a free-float M-LOK/Picatinny handguard, and the SIG Matchlite Duo 2-stage flat trigger gives a cleaner pull than most factory AR triggers. At 118.4 oz (7.4 lbs), it matches the weight of many direct-impingement rifles despite carrying the additional mass of a piston system. The QD suppressor-ready flash hider on the 1/2x28 threads is designed for SIG's SRD line of suppressors, though any 1/2x28 can will thread on.
For buyers considering the Spear LT: it makes sense if you want piston reliability, a folding stock for compact transport, and AR-compatible controls without the compromises of a fully proprietary system. Owners who do not need the folding stock or piston operation can find similar accuracy in direct-impingement rifles at a lower outlay. The CZ Bren 2 Ms is the closest alternative in the piston-folding-stock category, though it uses a different magazine well and control layout.
Best For
Strengths & Limitations
- Folding stock eliminates the buffer tube, allowing compact storage at roughly 25 inches folded while still firing if needed
- Short-stroke piston runs cleaner than DI systems, particularly noticeable during extended range sessions or suppressed fire
- The SIG Matchlite Duo trigger, while decent factory, does not accept standard AR-15 aftermarket triggers due to the piston-driven operating group
- Proprietary handguard mounting system limits rail swap options compared to standard barrel-nut AR setups
- At 118.4 oz (7.4 lbs) unloaded, it matches heavier DI rifles despite using a polymer stock, so the piston weight adds up
Category Rankings
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Frequently Asked Questions
Does the MCX Spear LT accept standard AR-15 magazines?
Yes. The MCX Spear LT uses a standard AR-15/M4 magazine well and ships with one 30-round Magpul PMAG. Any STANAG or PMAG-pattern magazine will fit and function. The upper receiver and piston system are proprietary, but the lower is AR-compatible for magazines and most controls.
Can you fire the MCX Spear LT with the stock folded?
Yes. Because the MCX uses a piston system with no buffer tube extending into the stock, the rifle cycles normally with the stock folded. This is one of the primary advantages of the platform over traditional AR-15 designs, where the buffer tube prevents stock folding.