SILENCER SATURDAY #268: Why Is The SIG MCX The Best Suppressor Host Available?

Good afternoon everyone and welcome back to TFB’s Silencer Saturday brought to you by Yankee Hill Machine, manufacturer’s of the new YHM Turbo T3 rifle suppressor. Last week we discussed the challenges of suppressing super short rifle barrels and what you can do to mitigate the harmful side effects. Pro Tip – It’s called 300BLK. This week I will explain why I think the SIG MCX is the best suppressor host available for rifle cartridges. I am Pete, your resident suppressor fan, and I approve of this message.

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If you know anything about me after seven years and almost 2,000 articles here at TFB, one of my missions is to not come across as an elitist prick that knows what’s best for everyone. If you want to carry a $4K BBQ 1911 in a small-of-the-back-holster, this is America and you should be free to choose form over function every day and twice on Sundays. So when I use the terms ‘Best’ or ‘Ultimate’ what I am really saying is “I really like this and here’s why”. And since it is 10 freaking degrees outside today, you all get to hear me editorialize rather than see pictures and the specs of a new suppressor.

The SIG Sauer MCX platform is not a perfect weapon – we can discuss some areas that could use some improvement later on – but when it comes to suppressed carbines, rifles, and now battle rifles, this is currently as good as it gets. If I had to pick one rifle to take to the end of the world, it would still probably be a 5.56 AR-15, only because of parts availability. But if I had a few lifetime’s worth of replacement parts, I’m definitely picking a 9″ suppressed 300BLK MCX-SPEAR LT. Once we have a more complete adoption of the MCX and parts are just as available as AR-15 parts, the answer will be a definitive MCX.

Why? Zombies. And also for the reasons listed below.

Differing from the AR-15’s direct impingement gas operated system, the MCX platform uses a short stroke gas piston to autoload new rounds into the chamber and throw out empty cases. The gas inside the barrel and behind the bullet eventually makes its way out of the gas port and operates a piston system that is not connected to the bolt carrier group. Instead, the piston gives a short but quick push to an operating rod that goes on to cycle the action.

Also known as a tappet system, the short stroke gas piston reduces the amount of reciprocating mass in the action and doesn’t require the use of a recoil buffer. The result in the MCX is a smoother, lighter feel in terms of recoil. There is simply less mass to move and then slow down with each shot which gives the operator a smother cycle and faster followup shots.

Since the gas moves the piston and in turn the operating rod outside of the action, a short stoke gas piston system also runs cleaner than a direct impingement system. This is especially important when using suppressors since back pressure can send particulates into the gas system and barrel that can eventually effect reliability.

And no recoil buffer or buffer tube means that lightweight folding stocks can make the MCX a very compact platform that can be fired in the closed position. Actually, the collapsing stock or “brace” MP5-style system is highly underrated and worth considering if you are going for the smallest possible footprint.

The MCX features a two position gas regulation system that is accessible through the handguard. The left side in the down position is the suppressed or (-) setting, restricting gas into the piston because adding a suppressor can caused increased back pressure and in turn, higher cyclic rates. The right side of the selector in the down position is the (+) and is used for dirtier than normal actions and weaker ammunition. Even with the rise of forward-venting suppressors, the ability to control gas makes a difference in felt recoil and particulates getting into the action. And the system itself is robust and easy to use with a definitive click on either side.

Joining the functionality of the short stroke gas piston and the gas valve regulation results in greater reliability. I’d be a fool if I said the MCX is more reliable than the AR-15 – there are just too many variables to make such a definitive claim. But less internal mass getting pushed around and a succinct impulse stroke to cycle the action results in a clean and reliable system. I have thousands of rounds through by MCX rifles (yes, a sample size of one) and the only time I had a failure to feed malfunction was when I was using the wrong gas valve on the 6.75″ MCX with SIG’s new SLH high flow 300BLK suppressor. The 6.75″ PDW was built to be suppressed with SIG’s previous generation of SRD suppressors which created more back pressure and required a smaller gas port.

I change out a lot of muzzle devices and suppressor mounts every week and some of them rest up against, or even inside, the handguard. Most of the AR-15 handguard systems require removing multiple bolts or alignment screws. One of the simplest but handiest features of the MCX system is that the handguard is held in place by the front pivot pin. The MCX-SPEAR LT did add two bolts that help keep the handguard from flexing, but overall it is a simple process to remove and install in less than a minute, giving easy access to muzzle devices that are tucked up under the front sight.

Barrel swaps are also simple and only require unscrewing and re-torquing two bolts. Technically an AR-15 barrel swap should be done by an armorer, even though we all self identify as armorers anyway. If you are running the MCX suppressor handguards, you can swap barrels with their respective suppressors already mounted – everything slides off and back on easily.

All of that being said, if you love your AR-15, you can keep your AR-15. MCX upper receivers drop onto any milspec AR-15 lowers. For those of you lucky enough to own select fire lowers, you can take full advantage of the MCX’s short stroke gas system under high rates of fire – all while suppressed. The only tuning you may need is a click of the gas valve. And with the addition of a small receiver extension to your AR-15 lower that includes a picatinny rail section, you now have your choice of folding stocks.

The MCX-SPEAR LT lower receivers also allow for the use of any of your favorite AR-15 triggers if you choose to make the switch. But I have never felt the need to change out SIG’s match trigger. Grips are also compatible with AR-15

If SIG were to ask me (and they aren’t) the MCX can benefit from a low carb diet and an extra day at the gym. All things being equal, the MCX will end up being heavier than it’s AR-15 cousin. As a suppressor lover, I also thing that adding an additional stop on the gas valve may be beneficial – suppressed, unsuppressed, and extreme would give users a little more range for low powered ammo and dirty guns.

All of this may sound like and advertisement for SIG, and I guess it is – one that I don’t get paid to say. The SIG is simply my favorite rifle to shoot suppressed and I think other silencer fans will agree with me. Some of the guns I own are for protection and some of the guns I own are purely for fun and enjoyment. The MCX is one of the few exceptions that fits nicely into both of those categories.

Thanks for reading. Be safe, have fun, and we’ll see you back here next weekend for another Silencer Saturday.

• SLH300TI and SLH300TI-QD / 300BLK / Titanium / 8.8″
• SLH762 and SLH762-QD / 7.62 / Inconel / 7.49″
• SLX762 and SLX762-QD / 7.62 / Inconel / 7.4″
• SLX762C and SLX762C-QD / 7.62 / Inconel / 5.2″
• SLH762TIC / 7.62 / Titanium / 5.24″
• SLH762TI and SLH762TI-QD / 7.62 / Titanium / 7.49″
• SLH762C and SLH762C-QD / 7.62 / Inconel / 5.24″
• SLX556 and SLX556-QD / 5.56 / Inconel / 7.4″
• SLX556C and SLX556C-QD / 5.56 / Inconel / 5.2″