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RECOIL Exclusive: An Inside Look at Sig Sauer’s CSASS – The MCX-MR

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This week at SOFIC there have been a few contenders for the CSASS program on display. Today I bring you one that wasn't.

If you've been watching Sig Sauer's Instagram closely enough you may have already caught a brief glimpse or two. However, much like the famed Patterson-Gimlin “Bigfoot” film, clarity and specific details were vague and ambiguous. Today we'll show you something with certainty, but remember; this is a pre-production model, and some details invariably will change before it's officially rolled out. It's a tad dirty, as they've been shooting the hell out of it.

So, while the Sig Sauer CSASS is definitely part of the MCX family of weapons, there's far more going on than a simple caliber change. It's officially name the MCX-MR. You'll see it shares many of the features of the MCX but some parts are significant deviations.

Let's go through them.

The buttstock of the MCX-MR has the same styling of the MCX, but also has adjustable cheek height and LOP.



At first this appears to be a standard AR-15 type charging handle, albeit with an enlarged latch and further stylization.


But no, there are actually two separate charging handles on this rifle. The user can choose between them. Neither one reciprocates and they both can operate independently from each other.



MCX_CSASS008Note the steel reinforcement of the receiver where the charging handle attached. Also that cutout on the lower? Just there to keep down the weight.

MCX_CSASS009The trigger guard is similarly skeletonized in order to squeeze off the ounces.



The billet receivers are constructed of the same aviation grade billet, and there are steel pockets in the QD sockets to prevent wear. The theme of using replaceable parts for receiver longevity continues with the MCX-MR.

MCX_CSASS012Here is where you can start seeing the charging handle get weird. That's a top-view of the charging handle. Actually, it can be either the top or the bottom. Instead of having a latch on both sides, Sig Sauer chose to make it flippable. To switch to the other side, simply take it out of the rifle and flip it upside down.


Unlike the handguard of the MCX, which slides off after pulling the front pivot pin, the MCX-MR requires popping off two screws first.


The MCX-MR currently has a two position gas regulator (suppressed and unsuppressed). Positions are clearly marked, no doubt having guys like me who forget everything in mind.


Taking the MCX-MR down is a little different. A single recoil spring and guide first has to be removed after shotgunning it open. No double-spring setup here. Then the charging handle can be removed in the normal fashion, and all the guts fall out.


The FAL-esque charging handle remains in the upper receiver when field stripped. It can be removed via removal of a retention pin. The BCG looks similar to the MCX, with the major exception being the large single op-rod in lieu of the double spring configuration.


Buttstock attaches in the same manner as the MCX. Just like how the MCX can utilize a standard AR/M16 receiver if needed, the MCX-MR will work with an SR-25 lower receiver.




The MCX-MR weighs just under 9lbs (a requirement of CSASS). It features a 416 stainless fluted Bartlein barrel with a 1:10 twist. I'm told that even when hotter then hell, it'll push out a statistically significant group measuring out under 1MOA. I look forward to getting some trigger time with one and will certainly advise further once I do.

In the meantime check out Sig Sauer's homepage here, or follow them on Facebook or Instagram.

You can see what an earlier iteration of the rifle looked like back at the NSSF SHOT Show 2015 over on Soldier Systems Daily.

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