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The Sig Sauer MCX SPEAR in 6.8x51mm is the civilian and commercial counterpart of the U.S. Army’s XM7 rifle, which replaced the M4/M16 platform as part of the Next Generation Squad Weapon (NGSW) program. This firearm is a direct evolution of the MCX platform, representing a significant leap forward in small arms technology.

Sig Sauer MCX SPEAR 6.8x51mm Overview
Feature Description
Caliber: 6.8x51mm (.277 Fury)
Action: Gas-operated, short-stroke piston
Operating System: Rotating bolt, AR-style with ambidextrous controls
Barrel Length: 13″ (military)
Overall Length: ~34″, depending on barrel and stock
Weight: ~8.5–9.5 lbs (unloaded)
Muzzle Device: QD suppressor-ready flash hider or muzzle brake
Stock: Side-folding, adjustable
Magazine: 20-round proprietary steel magazines
Optics Compatibility: Full-length Picatinny rail

Key Mechanical Features
Short-Stroke Gas Piston System: Offers enhanced reliability and reduced fouling, especially under suppressed fire.
.277 Fury Hybrid Case Technology: A high-pressure round with a stainless steel base and brass body, designed to outperform 7.62 NATO in energy and velocity.
Fully Ambidextrous Controls: Safety, bolt catch/release, and mag release.
Modular Design: Quick barrel changes and adaptability to multiple calibers and configurations.

Ballistics & Performance
Metric: 6.8x51mm (.277 Fury)
Velocity: ~3,000 fps (135–140 gr bullet)
Energy: ~2,900–3,100 ft-lbs
Effective Range: ~500–800 meters (varies by mission and load)
Penetration: Enhanced armor penetration over 5.56 NATO

Military Pedigree
Selected by the U.S. Army as the XM7 Rifle to replace the M4. Intended to defeat emerging body armor threats and increase lethality at extended ranges. The XM250, its squad automatic weapon counterpart, uses the same cartridge.