If you’re anything like me, you find yourself spending way too much time planning your next gun purchase. There are so many resources to consider and it can be quite time consuming. If you’ve been considering the Sig Sauer MCX Rattler, then you need to read this article. I’ve taken the time to aggregate all the best sources of information on its performance, reliability, and the best upgrades for this rifle. Keep reading for more.
The Sig Sauer MCX Rattler has gained massive popularity in recent months. It is billed as the worlds most compact rifle. It was born out of a requirement by the United States Special Operations Command (USSOCOM) to replace their aging stock of 9mm sub machine-guns, with something more modern and capable. The Rattler certainly is that.
Sig Sauer MCX Rattler Overview
The Sig Rattler was developed to replace military style personal defense weapons that shoot pistol calibers. Sig created the Rattler to take advantage of the ballistics of the 300 Blackout cartridge.
This cartridge utilizes the same case length as 5.56, but packs a much bigger bullet. Most 5.56 NATO rounds vary between 50 grains, up to 80 grains in bullet weight. The 300 Blackout ranges from 110 grains, all the way up to 220 grains for some subsonic rounds. It should also be noted that the Rattler can fire higher velocity supersonic rounds, and low velocity, much quieter, subsonic rounds.
Sig Sauer offers the Rattler in both 5.56 NATO and 300 Blackout configurations. Due to the extremely short barrel length (5.5in), 5.56 NATO is going to lose much more velocity, and consequently maintain much less energy than a 300 Blackout chambered Rattler. Sig also offers the Rattler in a pistol variant, with ATF compliant braces, and SBR variants, if you want to pay for a tax stamp.
Sig Sauer MCX Rattler Specs
The first thing you’ll notice, when looking at the rifle, is it’s extremely compact size. When folded, the rifle measures just under 17 inches in length. This means you can easily carry this in a non-descript bag or back pack.
The other interesting thing to note, when we examine specs, is the 5.56 NATO Rattler is actually a third of a pound heavier than the 300 Blackout. You might think that a smaller caliber would be lighter than a heavier caliber, but Sig Sauer has something to say about that.
Sig Sauer MCX Rattler Reliability
Like any firearm, developed for a military weapons solicitation, reliability will be of primary importance. As you will see, this can cause some problems, that we’ll talk about a little further down.
In this excellent long term review by the The Firearm Blog, the author states that he fired over 3700 rounds through his Rattler without malfunction. There are several reasons for this reliability.
First, this rifle is 90% (wild ass guess) similar to Sig’s MCX rifle line up. This line of rifles has been around for many years, at this point. This means they have had the chance to work out the kinks in the system, and fix any known weak points.
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Secondly, most military piston driven rifles are over gassed. This means that the amount of gas being vented from the barrel into the gas piston system is in excess of what is needed to reliably cycle the action, in most cases. Notice I say in most cases.
For a combat rifle, that is going to be used in the harshest conditions, such full auto fire when dirty, an over gassed gun will overcome weapons fowling from extended fire. The only downside is that the shooter is going to experience a lot of gas in the face, especially if you shoot it suppressed. See the video below for more.
I don’t fault Sig for choosing to over gas their system, but it is worth pointing out that many shooters find the shooting experience less pleasant due to this phenomenon. Having shot the Rattler suppressed, I did not notice any gas in the face with subsonic ammo.
Sig Sauer MCX Rattler Accuracy and Ballistics
Most shooters, myself included, would think that a 5.5 inch barrel could not maintain much accuracy at any extended distance. Most reviewers are reporting quite the opposite.
In the previous long term review by The Firearm Blog, the author states that he is seeing 1.5 inch groups at 100 yards. This is good for any rifle, and excellent for such a compact rifle. If you watched the Tim Harmsen (Military Arms Channel) video above, you saw that he is achieving pretty amazing ballistics numbers out of the 300 Blackout Rattler.
In the video, he shoots a supersonic Fiocchi 125 grain round, and achieves bullet speeds of 1800 feet per second with a muzzle energy of 905 ft/lbs. This is in excess of double the muzzle energy of a 9mm bullet. Tim then tests a 200 grain subsonic round, and achieves 828 feet per second with 304 ft/lbs of muzzle energy.
This data really highlights the fact that shooting the 300 Blackout in subsonic yields about the same energy of a 9mm supersonic bullet fired from a handgun. The Rattler does maintain the advantage in distance however, due to the more aerodynamic shape of the bullet.
Sig Sauer MCX Rattler Options
Sig Sauer prides themselves on the vast array of configurations that their MCX rifles can be changed into. The Rattler is no different in this regard. The first consideration for any potential Rattler owner, is which stock they want to use.
As we stated earlier, Sig Sauer sells a few variants of the Rattler. For the short barreled rifle (SBR) variants, the Rattler is sold with a collapsible wire stock, and a folding metal stock. They are also sold with almost identical braces for those who don’t wish to purchase an SBR. Stocks are pictured below.
Sig MCX Wire Stock 
Sig MCX Rattler Folding Stock
Most reviewers find these stocks/braces merely adequate. You have to remember that they aren’t designed to be the most comfortable stocks you’ve ever felt. They are meant to keep the weapon length to an absolute minimum. You will also find that there are much better aftermarket options available in the next section.
The other big option is determining which caliber you want. Personally, I don’t see any reason to purchase this firearm in 5.56, unless you already have other rifles in this caliber and want to shoot the same ammo. The ballistics of the 300 Blackout are much better than the 5.56 cartridge, for the Rattler’s intended use.
Sig Sauer MCX Suppressors
Many prospective buyers of the Rattler will ultimately want to suppress this rifle, in order to take advantage of the extremely quiet subsonic rounds that this rifle can shoot. There is one problem with this. When adding a traditional baffled can to a rifle, it increases the amount of gas in the system. This means you get even more gas in your face. However, there is a solution to this.
A company called Operator Support Systems (OSS) makes a suppressor called the Helix. This suppressor is designed to vent the gasses forward. This means that you will not receive an incredible blast in the face every time you shoot this weapon suppressed (giggity).
In fact, this suppressor only increases bolt speed by 5% over normal operation. Theoretically, you can use this on a rifle that does not have a suppressor setting, and it should not alter normal function.
Sig Sauer MCX Rattler Upgrades
Because of the Rattler’s popularity, there are a myriad of options for upgrades and customizing your firearm to your liking. As I mentioned above, I believe the number one purchase should be upgrading the factory pistol brace.
If you like the side folding feature, then this brace from SB Tactical is your best bet
If you just aren’t a huge fan of minimalist stocks, and like more conventional AR/M4 style stocks, then I would recommend buying this adapter (pictured below) which will allow you to install any mil spec buffer tube and after market stock you desire.
The next order of business should be changing the grip on the Rattler. Most reviewers noted that, while the stock grip was incredibly compact, they felt like they were holding a broom stick in their hands. Luckily enough, a normal aftermarket grip will fit on the Sig Rattler. I’m partial to the Magpul grips myself.
When the Sig Rattler was first released, it had a pretty horrendous trigger. Sig has since remedied that situation with their Matchlite Duo trigger. However, if you want something even fancier, then you can install a very slick Geissele trigger.
You will definitely need to install a quality optic on your Rattler, as it does not come with sights. Because this rifle really shines at 100 meters and in, you should be looking at a quality non magnified optic, like the Trijicon MRO. If you want all the details on the MRO, then check out my review.
The next order of business would be installing a hand stop, or forward grip point, so you don’t accidentally Swiss cheese your hand. This can be a real issue with this weapon, because the fore end is very short. It’s not such a problem when shooting suppressed, but I still prefer a hand stop or similar device. Here are a few that I recommend.
There is a reason why these are angled grips. The first, is that putting a vertical grip on the pistol variant of the Sig Rattler violates federal law. If you have an SBR, then you can put whatever you want on your gun. Either of these additions should give you an excellent contact point, allowing you to pull the weapon into your shoulder, and keep your hand exactly where it should be.
For those wishing to use their Rattler at night, it would be beneficial to mount a light. Due to its small size, and limited rail space of the Rattler, I would recommend the Surefire Mini Scout light, with tape switch.
If you are a professional user, or anyone who expects to run night vision with this rifle, then I would recommend using something like the Unity Tactical Fusion system. This modular system allows you to mount night vision lasers, like the PEQ 15, while mounting a light closely to the the laser device, conserving rail space.
Sig MCX Rattler Final Thoughts
We’ve covered a lot of info on the Sig Sauer MCX Rattler, as well as the accessories you might wish to add to your own rifle. Personally, I think this is a very good firearm for a specific purpose. If you’re looking for a very compact portable weapon, that packs a rifle sized punch, then this is the gun for you.
If you plan on shooting this all day, then this may not be the gun for you, at least not without changing the stock, and likely the grip. Even in stock form, this gun would make an excellent home defense weapon, as long as you understand the penetration characteristics of rifle rounds in interior structures.
If you have any comments or questions, put them below. Otherwise get out there and get shooting!
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What is that weathers finish on that rattler pic and optic? I absolutely love that look.
Please advise.
Unfortunately I couldn’t tell you. That image was used with permission and isn’t my own. It looks to be a weathered cerakote however.
Best in-depth review I could find on this Rattler. The links to accessories was ideal. I have a SIG 762 can for my later MCX (not Virtus), and may sell it due to the gas issue w/Rattler. Have to decide 300blk or 556. I shoot 556 suppressed b/c it’s quiet, rounds are cheaper. Thank you!
Thanks Rick!
Just came back to re-read your Sig Sauer MCX Rattler review. Thank you! Yes, this is the best review I’ve seen out of at least seven. Sig just announced that pistol variants will ship without a brace, so I came back to check your recommendations. My back ordered 300 BLK should hopefully ship soon. Plan to use a DA Sandman K with it.
Let me know how that combo works. I’ve been toying with the idea of trying a Rattler with my Sandman K.