The SIG MCX Spear: A step into the future or a slip into past mistakes?

A person trying to knock the SIG MCX lineup would be someone stuck with a task of exceptional difficulty. At the core of the MCX we see a series of rifles that for more or less seem to integrate an AR-15 style of controls into engineering aspects that are more stereotypically found in western european assault rifles. The deletion of the buffer tube and the direct impingement action definitely proves this thought process. The net result, of course, was the net gain of a foldable buttstock, unimpeded by internal springs, in addition to the more simple and easy to maintain short stroke piston gas system. Interestingly, true to an almost religious adherence to AR15 controls, the unique and awkward T handle charging handle was left overarching the receiver, meaning that rifles like the MCX VIRTUS can be handed to a soldier who has never touched a gun other than an AR15 and run it as if there’s no difference between the two. SIG had american operators in mind with this line up and in my eyes it appears almost as a sort of stop-gap somewhere between a G36, ARX100 or SCAR16 and an AR15.

That’s beside the point, however; today we’re here to talk about the Spear.


I think I speak for most when I say the Next Generation Squad Weapon program can be summed up with one word: Underwhelming. On April 19th of 2022 the US military selected the Sig MCX Spear as the replacement for the M4 carbine – a strikingly abrupt departure from the favored AR15 platform of five decades past. The Spear is a weapon chambered in the proprietary 6.8x51mm, developed by SIG to squeeze out as much velocity as possible from a 16 inch barrel. To understand why this round was chosen by SIG, we first have to understand the purpose set forth in the NGSW program; namely that the usage of a 6.8mm diameter projectile was a requirement and that the intent here was to adopt a cartridge to punch body armor of the rapidly evolving armies of US near peer adversaries such as China and Russia. So following the rules and guidelines SIG simply set out to accomplish what it was asked to do: it created an over pressured cartridge with a bimetal, stainless steel reinforced case head to survive pushing a 135 grain projectile out of a 16 inch barrel at 3000 feet per second (a remarkable feat) and then in turn promptly rebuilt its MCX line around said cartridge. Keeping this in mind, I don’t want to sound like I’m coming down too hard on SIG when I give my critiques of the Spear – these are design aspects which the US military demanded and SIG was simply the entity bringing them an engineered solution. My critiques largely have to do with what I consider oversights of doctrine more so than engineering deficiency.

To put it frankly the Spear strikes me as a regression back to the M14, FAL and G3 mentality – it’s effectively a battle rifle – granted a much evolved one compared to the aforementioned platforms – but a battle rifle nonetheless. That’s not to say there isn’t a place for heavier caliber rifles in modern use, but to replace and phase out intermediate cartridges in their totality is going entirely overboard. The sheer pressure of 80,000 PSI going off in your chamber is enough to cause a visibly obvious stout and heavy recoil which necessarily decreases the frequency of aimed fire an individual combatant can put down range. As we learned from past conflicts, such as Vietnam, statistically, the force which can produce the greatest volume of aimed fire is going to be that which has the greatest advantage in maneuverability and flanking – factors that ultimately decide the result of basic infantry engagements. Other factors that affect maneuverability are weight – something the 6.8×51 definitely does not excel in. While I can’t find any official weight figures due to either current unavailability or my own failure in research, I can pretty much guarantee the 6.8 will outweigh not only any intermediate cartridge by an enormous margin but also 7.62×51, given that it’s running higher pressures and by extension more volumetric propellant.

On the topic of weight/maneuverability, what’s more is the Spear itself weighs 8 lbs 5 oz without the can, which for a battle rifle would be respectable, but compared to the 6.4 lb M4 is a hefty ~ 2 lb addition at minimum. Now this is more compounded by the fact that the Spear appears to be intended to be mass issued with SIG’s 3d printed SLX suppressor, which adds an additional 1 lb 3 oz, leaving us at a total of 9lbs 8oz for what your soldier of the future is expected to carry. Furthermore, to be honest with you, based off the stubby and short flash hider the gun comes with, I have serious doubts of the rifle’s ability to suppress the flash of the high pressured 6.8 cartridge pushed through just a 16 inch barrel without the SLX suppressor being thrown on top of it. To me this is really quite a shame, as muzzle flash in many cases is a very real danger in low lighting situations and can turn any shooter into a brightly lit target for any would be enemies. If my hunch is correct that would effectively necessitate the use of the additional weight of the suppressor unless we see an overhaul in the flash hider design.

So is this proprietary cartridge really worth it? Does it actually punch common body armor types and am I, as a shooter, just slow to embrace the new technology requirements for playing war in the modern era? Well, the Military Arms Channel decided to address this by launching a 140 grain 6.5 PRC projectile at 3000 feet per second into an NIJ certified level IV plate to simulate the performance of the similar 6.8×51 cartridge to see if this is really the body armor killer it is designed to be. The drum rolled result was… maybe. The cartridge ultimately failed to punch the armor on the first shot, granted it appeared to come close to doing so. Potentially, with the addition of a hardened penetrator projectile it’s possible that they may be able to just barely push something through a level 4 plate if they tried – but certainly not with any astounding speed or impressive terminal wounding ballistics. I fully appreciate the desire of militaries to pursue punching ceramic level IV armor, but at the end of the day the Spear really feels like too many positives forfeited in pursuit of a goal which it only half achieved.


It is not a bad rifle, per say, and is likely much better suited in the hands of designated marksmen, but not what I would be handing the bulk sum of troops in any military. Many others have echoed a similar sentiment of skepticism to me with statements like, “I fully assume we’ll be back to the M4 before we know it.” While body armor is becoming more ubiquitous it hasn’t become lightweight enough to go back to the days of old where men will be found covered head to toe in suits of it. It’s my opinion that good, consistent, aimed and fast fire will still maim and kill with or without being able to punch the plate strapped around a torso.

That being said I’d love to hear other opinions. If you think I missed something, I’m an idiot, or you just have a better take on the topic feel free to let me know in the comments below. Truthfully SIG did a good job in what they were asked to do, so props to their engineers for that. I simply ask if the military itself is asking the right questions.

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