SIG MCX upper on M16 lower...It's Alive!

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  • Daezee

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    Installed a Parker Mountain Machining sear trip lever in my 11.5" 5.56 MCX upper (SIG will not sell this part to civilians even with proof of full auto ownership). It connects the MCX bolt carrier to the auto sear in the M16 lower. In and of itself, it doesn't make a full auto firearm, a full auto lower is required. The MCX upper comes already machined for the trip lever.

    Installed a Geissele SSF trigger group in my M16 lower so it would fire with the MCX upper (GI M16 trigger group would not push the firing pin lock out of the way to allow the SIG firing pin to be hit by the hammer).

    Removed the A2 stock and buffer assembly from the M16 lower.

    Installed the SIG MCX to AR adaptor in the M16 lower.

    Pull all together and dry fired functioned check...all good.

    Fired 40 rounds today in full auto in burst from 2-10 rounds...perfect functioning! Semi auto functioned as it should. Bolt locked back on empty mags. Examination of all parts showed nothing wrong.

    I certainly didn't "need" to take on this challenge. I figured since the MCX and AR trigger groups and takedown pin positions are the same/similar, to mate a MCX upper to M16 lower and have it function might be possible. I'd seen so many SIG Shot Show and advertisement videos showing full auto MCX firing, that I decided to figure out what makes it possible. Watch enough SIG videos and here and there if you freeze the video you can get glimpses of what's inside the full auto MCX. What really made it possible was an after market company making trip levers, SIG giving me an MCX upper to AR lower adaptor, and friends helping with building and experiments.

    For all the pics or it didn't happen people, kendive will be making a video of MCX full auto firing soon.

    In the upper picture, to the right, is the trip lever sticking out where it will contact the auto sear when mounted on the M16 lower. To the left is part where it contacts the bolt carrier. The bottom pic shows it put together with a SIG folding stock folded. The bbl has a Midwest Industries blast diverter on the end of the bbl to help throw the sound away from the shooter and others shooting on each side. Takedown of the upper remains the same...the bolt carrier group simply slides out. On a semi auto lower, the trip lever does nothing...just sits there not moving. On a full auto lower, when the selector is set to AUTO, the auto sear will be moved and come in contact with the trip lever working with the auto sear spring.

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    Little Jack

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    Jealous.

    Is the adapter two parts? I've not seen one in person and was trying to figure out how you got the shelf over the top of the buffer extension and got the bottom detent into the lower.
     

    Daezee

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    Adaptor is 4 pieces. Screw threaded part into the lower where a buffer tube would normally screw in. Hold back (large part with picatinny rail) part in contact with back of the threaded part. Drop buffer piece into front of the threaded part. Drop bolt in the hole in the threaded part...bolt goes through buffer and threaded part and screws into the back part holding all together.

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    B52

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    Dam it, now there is something else I want and it's all your fault. Luckily some parts are made of almost-unobtainium. The slightly more common isotope of unbotainium. Daezee, I look forward to videos of you shooting your latest, Marry Shelley creation? Also the comments when you post on AR15.com

    Nate are there any deals on SIG uppers?
     
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    Little Jack

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    Dam it, now there is something else I want and it's all your fault. Luckily some parts are made of almost-unobtainium. The slightly more common isotope of unbotainium. Daezee, I look forward to videos of you shooting your latest, Marry Shelley creation? Also the comments when you post on AR15.com

    Nate are there any deals on SIG uppers?

    I don't have a source for MCX uppers. I've seen them on GB but I think they're still a little on the high side. Cheapest I've seen is $900 for a complete one but can't get confirmation on which has block/carrier it is
     
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