KNS Precision AR-15 Buffer Tube to SIG MCX Stock Adapter

Hrachya H
by Hrachya H
KNS Precision AR-15 to SIG MCX Stock Adapter

SIG MPX/MCX stocks have become a popular accessory not only for the SIG firearms but for other guns, too. There are multiple different adapters designed for these stocks such as those made by JMac Customs. Recently, KNS Precision has announced that they now make a similar adapter for AR-15 buffer tube replacement.

KNS Precision AR-15 to SIG MCX Stock Adapter -11

First things first, this adapter is not compatible with AR-15 pattern rifles because it replaces the receiver extension. The KNS Precision AR/MCX adapters should be used with those firearms that have a provision to mount an AR-15 buffer tube but they don’t have a mechanism inside the buffer tube and can function without it. There are many weapons that use the AR-15 buffer tube to make it possible using the AR-15 stocks – AKs, shotguns, bolt-action rifles … you name it.

The AR/MCX stock adapter consists of a threaded base part that replaces the AR-15 receiver extension, a Picatinny rail section that becomes the mounting platform for the MCX stock and a hex screw with a lock washer that attaches the rail section to the base.

KNS Precision AR-15 to SIG MCX Stock Adapter

The KNS Precision AR/MCX stock adapter is available in two versions: flanged and non-flanged. The flanged version should be used with those weapons that utilize AR-15 style receivers and need some mean to secure the takedown pin detent and its spring in place. So, basically, the flanged adapter also replaces the AR-15 endplate. For all other firearms, you can use the non-flanged version of the adapter which has a more slimline profile.

AR/MCX ada[ters without (left) and with a flange
KNS Precision AR/MCX stock adapters are listed on the company’s website at an MSRP of $60. The price is identical both for the flanged and non-flanged versions. The company also offers an AR/MCX adapter and MCX stock combo kit at a price point of $180. There is also an adapter kit for the CZ BREN 805 rifle ( MSRP-$220) that includes a Bren to AR-15 stock adapter, an AR/MCX adapter and an MCX stock.

Images courtesy of KNS Precision,

Hrachya H
Hrachya H

Managing Editor Being a lifelong firearms enthusiast, Hrachya always enjoys studying the history and design of guns and ammunition. Should you need to contact him, feel free to shoot him a message at

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14 of 26 comments
  • Sunshine_Shooter Sunshine_Shooter on Nov 28, 2018

    So, what guns use a mil-spec lower but don't need to reciprocate into the buffer tube?

    One guy below said a dedicated .22lr would work, but what else?

    • See 10 previous
    • Wow! Wow! on Dec 01, 2018

      @Sunshine_Shooter Serbu SU-15 upper, as well as homemade SMG uppers like outlined in Bill Holmes 9mm AR book.

  • DanGoodShot DanGoodShot on Nov 29, 2018

    So can I use this on my AR15? It's a 300 blackout, not .223 rem. 🐒