what is an AR-15?
The only correct rubric is to look at Eugene Stoner’s original design, which means that at a basic level, the AR-15 is a direct gas impingement operating rifle. The upper and lower receivers hinge together, and the bolt carrier group is returned by a recoil spring that goes back into the buffer tube.
To me, any deviation from this design means the rifle is no longer an AR-15.
MCX next to an actual AR-15
Let’s compare the MCX to an actual AR-15. From the same manufacturer, the SIG Sauer M400 SDI X-Series is an actual AR-15 design. The rifle is a direct gas impingement AR with all the features and design principles that make up the AR-15.
I did a full review on that rifle, and I stand by my statement that it is one of the best out-of-the-box ARs on the market. But how does it compare?
Both rifles are chambered for 5.56. Both have 16-inch barrels, similar controls, similar rail designs, and take the same pattern magazines. While they share a physical aesthetic, the deeper you dive, the quicker you realize that they are not the same at all.
what is the difference?
First, the SIG MCX is a short-stroke gas piston firearm, very similar to the M1 Carbine and the SKS. The gas is redirected onto a rod that sits over the barrel. The gas forces the rod forward just enough to tap the bolt carrier group back into the receiver. This ejects the spent casing, and the springs return the bolt to the chamber as it picks up the next round.
Additionally, the upper does not feature a buffer tube or buffer tube spring. Like the AR-18, the MCX bolt rides under springs that span the length of the upper, allowing the entire system to be housed in the upper assembly. This shortens the overall functional length of the firearm and gives the lower the ability to mount any kind of stock, as the stock no longer plays a pivotal role in operation.
Is it better than an AR-15?
The MCX’s operating system has several advantages. For example, the MCX’s gas system runs a tad cleaner than a typical AR-15. Without that gas being redirected directly in the chamber, the firearm can go for longer periods between cleanings. While this does not inherently make the firearm more reliable, it can increase the longevity of reliability.
Another benefit is discovered when you add a suppressor. As suppressed shooting continues to rise, most AR shooters can attest to the unpleasant “onion cutting” tears that accompany long days of shooting AR-15s with suppressors.
In the MCX’s operation, the gas is bled off at the gas port, farther away from the chamber and the shooter’s face. While there can be a more audible pop from the gas expanding at the piston, the tradeoff of a tear-free sight picture is worth it.
It is difficult to answer whether the design is objectively better; however, it speaks volumes that the overall design was selected by British SAS and U.S. SOCOM forces.
My initial opinion
I’ll be honest: I thought the MCX was an overpriced gimmick for a very long time. I typically stay away from piston-driven 5.56 firearms, and I saw the MCX as an expensive piston-driven AR.
In my opinion, the biggest benefit of shooting 5.56 is that the cartridge is so soft in its recoil impulse. Especially considering 20-inch barrels and rifle-length gas systems, the AR is so easy to control.
When you take that cartridge and place it in a short or long-stroke gas system, the recoil is much more noticeable. Now, I’m not saying I can’t handle it – it’s just that during long days of shooting controlled pairs, training, and drills, I want my dot to hop around as little as possible.
All the little things make the difference when it comes to the efficacy of your training. Eliminating as many variables as possible helps keep my performance more consistent. I have shot thousands of rounds in piston-driven systems, and my experience has left me preferring direct gas impingement 5.56 designs.
My experience and opinion change
Last year when I was touring the SIG Sauer facilities in New Hampshire for SIG Freedom Days, I was offered a chance to shoot the new MCX Spear LT at the indoor training range. I politely declined the offer from the range master, thinking that I had shot plenty of guns that day, and I wasn’t interested in a piston-driven AR-style shooting experience.
The range master was adamant that I at least try it and give honest feedback. He even offered a few magazines of free ammo to entice me. Who am I to pass up some free ammo? I decided to try the firearm so that I could inform him that I thought it was an overpriced AR.
I shot about five magazines and was instantly humbled, realizing I had too quickly formed an opinion before I had experience with the system. I immediately called my brother’s gun shop back home and told him I needed to order an MCX.
I was a skeptic, but let me tell you, it is a dream to shoot. Like a finely tuned sports car with a rough, off-road construction, the MCX is a well-built and incredible performing AR-style rifle. See what I did there? Not an AR-15, but an AR-feature-rich design.
There is almost no recoil on the short-stroke gas piston, having a similar recoil impulse to that of the M400 SDI X-series. The suppressor pushed almost zero gas back into my face, and I could easily shoot tight groups on multiple targets.
Since then, my MCX pistol has become my go-to firearm. From contracting to home defense, I have spent a lot of time training on the system, and every round has been a pleasure.
So, is it an AR-15?
