Sig MCX Rattler / M13 Suppressed

Have you ever looked at your .300BLK and thought it’s just a little too big or a little too loud? Not super likely, but Sig has an option for you anyway. Garand Thumb takes a deep look into the Sig MCX Rattler, (or in the gamer realm—the M13), and tells you why you should consider this one.

The Sig MCX Rattler is essentially a .300BLK on an M4 platform, with all the controls being virtually the same. With the same controls and functions, the Sig MCX is an easy-to-learn rifle, according to Garand. His thought is that some version of this weapon will be the next one adopted by the military.

He starts by going over the technical details of the rifle. It has a very short 5.5” barrel. With being that length, Garand says that the fired round only touches a little over 3” of the barrel. It’s a short-stroke gas-piston-operated platform that is very similar in design to an AR18.

Both Sean and Garand believe that due to the modularity of the Sig MCX Rattler, that some version of this weapon will be the next one adopted by the military.

Sig MCX Rattler — Review


They feel that the system is very cool. They say that there isn’t anything exactly new about the MCX, it’s built off the existing systems that already work. They, Garand and Sean, say that the weapon is very prevalent in video games due to the modularity of the system. You can take the rifle as is, or you can swap out just about everything on it, from the rails to charging handles to buffer tubes and it will still run without hiccups. When it’s compared to an AR15, this one is built from the ground up to be modular.

Suppressor Recommendations

With the rifle being from Sig, you’ll probably use a Sig suppressor on it, but regardless of what you choose, Garand recommends using a direct thread. The rail that comes with the rifle is short and he chose to install a longer rail to one that covers the suppressor. His main comment with that is that it helps keep the barrel from flexing if you happen to be leaning up against something while shooting, which we all know will damage the system if you do that.

Gas Block Access

Even with a longer rail, which gives you more accessory mounting options, it doesn’t interfere with the system or the ability to access the adjustable gas block. That’s right, there is an adjustable gas block built into the system that can be adjusted for rate of fire, gas bleed on the system, or what have you, all on the fly. Not only that but there are markings on the receiver itself to tell you which way to turn for adjustments. They both say that feature makes the weapon “Army proof”.

Sig MCX Rattler at the range
Garand and Sean can’t stress enough just how modular this rifle is, saying it was built from the ground up to be customized to the end user’s needs, from suppressors, rails, or stocks.

.300 BLK

While the 5.5” barrel isn’t ideal for a .300BLK, it is very reliable. The point that Garand keeps coming back to is that the weapon is super modular. The rifle can shoot both sub- or supersonic rounds, all with minor adjustments from the aforementioned gas block. He really likes the .300BLK round and this rifle, even if the round doesn’t always have the range when compared to a 5.56. He thinks that it is a great military rifle with a gentle recoil and is extremely quiet when shot suppressed. The sound of the round hitting the target is actually louder than the cycling of the rifle.

Recoil and Blowback

The rifle also does a great job of dissipating the gas within the system. It’s funneled back and then down into the mag well. With very little blowback in the face, it’s very enjoyable to shoot. With the dissipation, the recoil is very insignificant. Piston guns generally have more recoil, just because of the design, but this one is very gentle.

Garand Thumb shooting the Sig MCX Rattler.
With the help of the built-in adjustable gas block, both supersonic and subsonic rounds can be shot through the Sig MCX with only minor changes. To Garand, it is a very soft shooting but a very accurate system.

Garand does mention a couple of things that he didn’t like:

1. The brass deflector is made from polymer. This is a problem in the long run as it will get eaten up by ejected casings and will probably need replacement.

2. Subsonic rounds don’t run well through non-.300BLK magazines. He recommends either Lancer or Magpul mags.

Garand Thumb
Garand Thumb reviews the Sig MCX Rattler.

Garand rounds out the review with talk of the stock. The stock attaches at a 1913 rail, giving way to plenty of options. With the collapsible stock, it’s only 16” without the suppressor and very concealable under a car seat or bugout bag. Like everything else on this weapon, it is
simple and very easy to swap things out.

Garand, and Sean, close out the video by saying that it’s a very cool gun that is super fun to shoot. But just like with any weapon, you need to train with what you have, saying: “All cool dudes get training”.