What's the best 9mm ar lower?

Gaujo

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Considering building a 9mm ar, and curious what the wisdom is on the lower. I have normal ar-15 lowers available, and trying to see if it's worth going through the trouble for dedicated 9mm magwell?

This would be for a CMMG Guard Radial delayed build.

I see these CMMG pmag adapters, but at $30 each, it's got me wondering if it's worth just getting a glock lower or something.
 

fortyfive1911a1

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Considering building a 9mm ar, and curious what the wisdom is on the lower. I have normal ar-15 lowers available, and trying to see if it's worth going through the trouble for dedicated 9mm magwell?

This would be for a CMMG Guard Radial delayed build.

I see these CMMG pmag adapters, but at $30 each, it's got me wondering if it's worth just getting a glock lower or something.

I strongly recommend the Hahn mag well adaptor that uses Colt pattern mags. Particularly nice if you have a registered lower.

https://hahn-precision.com/ar-15-top-9mm-adapter/

The Stern mag well adapters also work well, though I’m partial to my Hahn adapter.
 

A&S Conversions

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Personally I would use the MEAN Arms incerts https://www.meanarms.com/products/detail/endomag-9mm for the CMMG RDB upper. The standard Colt style blowback system needs the Colt or Glock style mag about 0.010" higher than the RDB system. So unless you can find a CMMG specific magwell adapter, you will have to shave 0.010" of the mag catch. The Endomag puts the mag right where it needs to be for the CMMG upper. With the Endomag incerts you don't have to mess with a magwell adapter. Just use a standard lower you already have. I would suggest using Generation 3 Pmags. With Gen 2 Pmags it is hard to get the last couple of rounds into the incert. Gen 3 doesn't have that problem. Yes the Gen 3 Pmags plus the incert is more money per mag, but you don't need to buy a dedicated lower nor deal with the magazine height difference.

Scott
 

amphibian

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Personally I would use the MEAN Arms incerts https://www.meanarms.com/products/detail/endomag-9mm for the CMMG RDB upper. The standard Colt style blowback system needs the Colt or Glock style mag about 0.010" higher than the RDB system. So unless you can find a CMMG specific magwell adapter, you will have to shave 0.010" of the mag catch. The Endomag puts the mag right where it needs to be for the CMMG upper. With the Endomag incerts you don't have to mess with a magwell adapter. Just use a standard lower you already have. I would suggest using Generation 3 Pmags. With Gen 2 Pmags it is hard to get the last couple of rounds into the incert. Gen 3 doesn't have that problem. Yes the Gen 3 Pmags plus the incert is more money per mag, but you don't need to buy a dedicated lower nor deal with the magazine height difference.

Scott

+1, I would go with the MEAN Arms Endomag inserts.
When the CMMG RDB first came out, I got their lower to run with Glock mags to make sure everything was going to work out.

I'm not crazy about Glock mags so then I modified my Hahn block to work with Colt mags as I have documented here:
https://c3junkie.com/?page_id=374

Then when the Endomags came out I've been running them ever since.
https://c3junkie.com/?page_id=280

I like being able to swap uppers on the same lower...which really helps if you have a select fire lower.
No messing w/ removing a mag block.
Also if you have an expensive trigger in your lower, you don't have to buy another one to put in another lower.

NoWeightBaseline622RPM-1024x486.jpg


However, if you haven't purchased the CMMG RDB BCG/BBL yet, I would wait to see if anything substantial is announced at the Shot Show. I've been waiting on the MEAN Arms 'bearing delayed blowback' which was supposed to ship last quarter 2021. I'm hoping it comes out soon as I am hoping it won't have the ejector failure issue that the CMMG RDB has.
 
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chili17

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amphibian

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Yes, MEAN Arms invented it and CMMG re-sells the Endomag. Last time I checked CMMG only re-sells the RDB version and not the straight blowback version w/ the built in ejector.

It is a different feed height because it just works out that way with a barrel extension....
Look at the gas operated uppers that Macon Armory and RMW make....it is the same thing...
both of them require lowering the mag height for them......and you can use a lower that works for their gas operated .45's OR for the CMMG RDB's as they both use extensions w/ rotating bolts.

What is really going on is putting the mag height back the way it should be....same height as a 556 mag.....instead of straight blow back which I think is an abomination..
 

Member13

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I went with the Aero Precision EPC-9, mainly cause I already have a million glock mags. Plus it has LRBHO and I found upper and lower for less than $200 total. I haven't assembled it yet so no real feedback from me but there are lots of sources out there.
 

Captain murrica

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I went dedicated 9mm lower, one cmmg and one YHM and I Like them both. There’s no adapter to screw with and built with 9mm shell deflector and ejection port door. I went colt pattern because I’m not a Glock guy. Just my .02, I have no experience with other 9mm setups.
 

Jmacken37

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For the AR, I find the "amphibian setup" with endomags hard to beat in terms of smoothness and reliability. I don't think I've ever seen a factory setup AR 9mm subgun make it through a subgun match without crapping the bed.
 

A&S Conversions

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For the AR, I find the "amphibian setup" with endomags hard to beat in terms of smoothness and reliability. I don't think I've ever seen a factory setup AR 9mm subgun make it through a subgun match without crapping the bed.

That depends on how it was done. My first machinegun was a Colt M16. I spent so much time and effort trying to get it to run in 9mm reliably. I always had some kind of issue, mostly relating to pushing the mag in too hard. This would make the drop in magwell adapter get shoved up in to the bottom of the 9mm bolt. That would cause the ejector to rub the bottom of the bolt causing malfunctions. I found a DIAS. I used that in a Colt LEO marked 9mm. Just before the '94 ban, Colt was pinning steel sear blocks into their lowers. After the ban up until around '99, Colt did not put sear blocks into the LEO marked lowers. After the ban ended I found a gray LEO marked 9mm carbine without a sear block that was drilled for the front push pin. I used the DIAS to convert it. It always ran great for me because the 9mm magwell adapter was pinned in, at the factory. Of course around the same time I bought the DIAS I bought a Vollmer converted 94 that was married to a Fleming sear. The converted 94 was so much smoother than the Colt 9mm. I would use the Colt occasionally with my Garrison DOE upper. But mostly I used the converted 94.

Scott
 
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