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SIG SAUER’s adding a suppressed upper receiver to their lineup: the SUR300. The new upper — chambered in the ever-so-chic 300 blackout (300blk) — fits the SIG MCX and a standard AR15 lower. The MCX upper has some cool features:

– 6.75” Cold Hammer Forged Barrel

– Permanently Attached 19 Baffle Titanium Suppressor

– Free Float M-lok Handguard

– Short Stroke Gs Piston

– Tunable Gas Block

– Cycles Sub and Super Sonic Ammo


It also comes with SIG’s Matchlite Duo two-stage trigger, as well as an adapter that lets you remove the buffer tube and accept SIG 1913 folding stocks.  Bolt and charging handle are included.




“This is a new OEM Sig Sauer MCX Conversion Kit that includes an integrally suppressed MCX upper receiver, adapters to convert the lower receiver to accept the MCX upper receiver, and a Sig Sauer two-stage trigger. The trigger installation is required to ensure proper operation of the MCX upper receiver. Using your existing trigger is not recommended and may lead to malfunction.

The suppressor is pinned and welded meaning that the overall length is just over 16”. Putting this on your rifle will not make it an SBR.

Note: All NFA Rules apply. This item will require a Form 3 transfer to your local dealer and then a Form 4 transfer to you. Make sure you can legally own this item before purchasing.”



UPC Code: 798681605811

Caliber: .300 Blackout

Manufacturer: Sig Sauer

Sights: None

Frame Finish: Black

Barrel Length (in): 16.8 in OAL

Accessory Rail: Not Applicable

More from The Truth About Guns:

Gun Review: SIG SAUER MCX Rattler SBR

Hands on with the new SIG MCX Virtus

Gun Review: SIG SAUER MPX Copperhead 9mm Pistol

Gun Review: Lone Wolf G9 AR-15 Lower Receiver for GLOCK Magazines

Gun Review: Fulton Armory FAR-15 USGI A2 Upper Receiver Assembly

New From FightLite Industries: STEP-22 Receivers and Integrally Suppressed Ruger Receivers

SIG SAUER Announces 3.5-Inch Barrel MPX Copperhead 9mm PDW

300 AAC Blackout: Belle of the Silencers Are Legal Ball

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  1. Will the AR adapter accept an AR buffer tube adapter? Second question… If so, will attaching a buffer tube to the adapter on the adapter create a singularity that leads only to the ATF office?

  2. I plan on getting an integrally suppressed .300 BLK upper soon. I’ll wait to see what the price is on this. I’ve been looking at that one that’s advertised here on TTAG as well. It’s cool that stuff like this is commonly available now, but there’s even competition in the market. It really wasn’t long ago that all this stuff wasn’t available.

    • SOCOM’s SURG contract (suppressed upper receiver group) is the cause of all of these integral AR uppers we’ve seen in the last year. The GEMTECH Integra was pretty awesome in 5.56 (it’s reviewed on TTAG) and I hear it’s crazy quiet in 300 BLK. LaRue has an interesting looking one. This SIG one shows promise. The Thunder Beast Arms one I shot a few weeks ago was sweet. There are others, too, of course, and there will be more new ones releasing this year.

      • Thanks for the reviews on these things. I’m probably going to get one if silencers ever get out of the NFA. If they don’t when I get around to getting a silencer, I’m probably just going to sbr the lower or put a brace on it.

        At the rate I’m buying “not silencers” gun stuff, it might be a couple of years before I can afford any kind of decent silencer.

  3. Two things….no word on OAL. If it’s less than 16”, it’s a 2 stamp piece unless put on a pistol lower piece. And finally and most important, integrally suppressed means a ported and tuned barrel. No indication here that’s what this is. It might just be a suppressor welded on to a barrel. In which case, it’s an inferior offering. I’ve been cajoling barrel manufacturers to offer stand alone, properly integrally suppressed barrels with an OAL of 16” for over a year now. No luck yet. Faxon should do it.

    • Not to be a contrarian but an integral suppressor does not necessarily mean that the barrel is ported, only that the suppressor is integral to the operation of the firearm. Yes many designs like the MP5SD do have ported barrels but a ported barrel does not always reduce sound signature.

      My buddy is part owner of a company called D3 that makes an updated AR15 version of the MP5SD (check out their videos on YouTube). For 9mm it makes sense to port the barrel since removing a small amount of gases will lower velocities to subsonic. I guarantee you that if you look at an integral 5.56 there would be no ports as that round is traveling way too fast to bring it down to subsonic velocities and it would actually make the suppressor louder.

      I had asked my buddy about doing a custom build with a 300blk integral suppressor and asked him about porting the barrel. In all his testing, a ported 300blk barrel always made the integral suppressor louder, but ported barrels do work well for things just above the sound barrier like 9mm/22lr etc.

      • “but ported barrels do work well for things just above the sound barrier like 9mm/22lr etc”
        I have a CZ 452 integral that begs to differ. Manufacturer stated that it is ported to work best with CCI SV and boy is he correct. Sub MOA and all you hear is the action and the bullet hitting the berm.

  4. “The supper [sic] has some cool features.” I don’t understand. If you wrote that, correct it. If an editor caught it and inserted the sic, change it.

    Sic refers to a mistake/unusual usage that was in the originally quoted material that is not a mistake/unusual usage of the person quoting it.


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