We Take a Closer look at the SIG Sauer MCX Rattler PSB

   09.04.18

The Sig Sauer MCX is a rifle that has been in development for a long time.  While it was officially released to the general public in 2015, SIG had been developing the weapon for many years before then.

The MCX is actually a rather unique firearm, because it essentially merges certain components of the AR platform with the gas system of SIG’s own MPX.  In fact, with the proper adapter, it’s even possible to use the MCX upper with an AR lower.

Why was the MCX designed?  The short answer was for America’s special forces.  The aim was to create a lightweight rifle that could fire rifle ammunition as quietly as a submachine gun such as the HK MP5, while also being more modular than any other kind of semi-auto/automatic rifle ever designed.

In case, you haven’t noticed, SIG has definitely been getting into modularity in the last few years.  The P320, for example, is a mostly modular pistol and that one of the primary reasons the United States military chose it as their next service pistol to replace the Beretta M9.

SIG wisely designed the MCX to make it as comfortable and convenient as possible for shooters of the AR-15.  In other words, the two rifles handle and fire extremely similarly so that transitioning between the two platforms is rather simple.

But while the main MCX model is a full length rifle like an AR-15 or AK-47, one unique model of it that deserves special attention is the MCX Rattler PSB.  This is a much smaller and more compact version of the MCX that is designed primarily for personal defense.


The MCX Rattler has a barrel length of five and a half inches with a PDW upper.  This translates to an overall length of just sixteen inches when the stock is folded.  A good comparison, in terms of size, would not be to assault-type rifles but rather to submachine guns.  The MCX Rattler is only a few inches longer than the extremely compact HK MP5K submachine gun, for example.

In SIG Sauer’s own words, they designed the Rattler to be “as discreet as possible while retaining all of the capabilities of the MCX.”

The MCX Rattler also features an M-Lock hand guard, flash hider, an aluminum folding stock, and the ability to easily attach a suppressor.  It’s also currently only chambered for the .300 Blackout round, per the PDW specifications put forth by the United States military that SIG designed the weapon from.

Sig Sauer MCX 1
5.5″ Barrel with PDW upper

Currently, the Rattler is available in two basic configurations: the PSB model and the SBR model.  The difference between these two is that the PSB has a three position pistol brace while the SBR has a folding stock.  The SBR version is only legal for civilian use with a tax stamp from the ATF; however, the PSB version can by owned legally be civilians without the tax stamp thanks to the pistol brace feature.

The basic purpose of the pistol brace is to extend the length of the weapon to make it legal to own in accordance with current government regulations, while also making the weapon easier to control.

Basically, the brace wraps around your firearm beneath the elbow to help stabilize it when shooting.  It also allows the user to effectively wield the weapon with one hand.

Sig Sauer MCX 2
3 Position Telescoping PSB

As the MCX Rattler is only available in the .300 Blackout caliber, only time will tell for if SIG will one day offer it in the 5.56x45mm NATO caliber as well.  There’s no doubt that many people would highly appreciate SIG to offer the MCX in that caliber, including the MCX Rattler PSB.

So, why would you want to own an MCX Rattler PSB?  After all, it’s a highly expensive weapon at around the $2,500 mark, so how would owning it justify the cost?

The MCX Rattler PSB would be best utilized as a home defense weapon, thanks to its smaller and compact size that allows it to be effectively wielded in tight conditions while also firing a rifle caliber (in this case, the .300 Blackout round).

The advantage here is that you’re getting a more powerful gun than a pistol caliber carbine but in the same package.  You’re also getting the big advantage of having the brace, which makes the firearm much easier to control as well.

Does this mean that the Rattler PSB is the ‘ultimate home defense weapon?’ Not at all, but it is to say that it is definitely one of the most advanced options on the market.

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