SIG MCX: When is an AR not an AR?

As many of you may know, SIG has been working on/rumoring about a rifle modeled after the MPX for awhile. Well, the gun has officially been released and it is called the MCX.

Cabela's apparently got in an entire shipment and might possibly be the only available outlet for these new guns. That's just a guess on my part but I say this because I've seen none on gunbroker and neither Osage County Guns nor Bud's is showing it on their websites.

The MCX is currently available in a 16" format as well as a pistol format with SIG arm brace. Guns being sold by Cabela's come with a 300 AAC Blackout barrel installed and include an additional barrel in 223 Remington. Both barrels are complete, to include gas system parts.

I picked one of these guns up over the last weekend and swapped out the factory 3-prong for an AAC 51T on the Blackout barrel. Honestly, I don't need another 223 and don't even plan on using the other barrel at this point.

Anyway, I am going to refer--maybe incorrectly--to the MCX as an AR variant. The design isn't much like an AR internally but it does share some common parts and accepts AR magazines. Manual of arms is AR across the board.

The gun remains unfired at this point. I hope to rectify that this weekend.

http://tapatalk.imageshack.com/v2/15...c1ab2f3b30.jpg

How much are they at Cabelas?

Cabela's price is $2100 as the complete kit but they're currently running a sale. Save $200 until the 15th or 16th.

For the sake of your Canadian brethren, please don't refer to it as an AR variant, which it is not.
The wise Canadian federal gun control overlords, or police force I mean, determine the classification of new firearms based on a combination on a combination of factors, including, consulting tarot cards, emotional evaluations of a gun's scariness, "ease" of conversion to full-auto and determination of if a firearms is a "variant" of an existing restricted of prohibited design.
This last requirement has been notoriously used to declare the Armi Jager AP-80 as a variant of the evil and prohibited AK-47, and many other ridiculous examples.

Perhaps it a bit Off-Topic, but just throwing it out there.

I'd love to get my hands on one of these puppies.

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Originally Posted by Benito

For the sake of your Canadian brethren, please don't refer to it as an AR variant, which it is not.

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I doubt any Canadian gun control beaurocrat is going to be frequenting M4 looking for classification ideas. But we never know, do we?

Is derivative a better word? The gun does share some internal and external parts but the method of operation is different. The MCX is a piston gun and the bolt carrier is like an AR carrier up front but it has the rear end chopped off. This allows for a full cycling stroke inside the confines of the upper. Since there's no buffer tube the recoil spring (actually two springs in this case) have been affixed to guide rods that run at 10:00 and 2:00 above the bolt carrier.

Dimensionally it is supposedly possible to use an MCX upper on a standard AR lower with the installation of an adapter kit that will interface with the new recoil springs.

In execution, the MCX is quite similar to the Rock River piston gun. I messed with one of those rifles about four years ago. It showed some potential but didn't seem as well executed or as evolved as the SIG.


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The MCX has some very interesting and well thought out design features. I hope they can overcome their previous issues with slipshod QC/QA and release rifles that work. If these work and prove themselves reliable, I will definitely pick up a short upper to use on my M16 lower. Having been an early adopter of the 556, I will sit out the MCX until it has been vetted.

Are these designs from the former owner of AAC? I thought I read somewhere he was leading their R&D department.

Derivative, variant, inspired by, it's all fair game to anti-gunners.

I am a bit behind the curve on the latest developments in the world here. Is this thing at all compatible with AR lowers, or the MCX lower on an AR upper?

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Originally Posted by Benito

I am a bit behind the curve on the latest developments in the world here. Is this thing at all compatible with AR lowers, or the MCX lower on an AR upper?

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SIG is supposed to have a conversion kit available for the MCX upper on an M16 lower. I believe the kit will include a plug for the receiver extension hole as well as some type of backstop plate for the recoil spring guide rods.

As for using the MCX lower on an AR upper; I dont see how that'd work because there's no provision to attach a buffer tube.

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Originally Posted by rushca01

Are these designs from the former owner of AAC? I thought I read somewhere he was leading their R&D department.

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It would seem so.

The MCX has evolved somewhat since this video was taken. Probably the most notable change is the switch to a self-regulating gas system.

SIG MCX LVAW Multi-Caliber Piston AR Assault Rifle/Carbine/SBR Family Ex...: http://youtu.be/H3-bB1RCU4Q