AR9: Anyone have a Stern adapter (glock) or a AR glock lower to measure?

[smdub]

I've been tinkering this winter trying to build a better AR9. We're just not happy with the mag choices (mostly their reliability.) We really wish someone would make the equivalent of Black Dog AR15/22 mags (one piece, metal feed lips, AR15 form factor, no adapters, and they 'just work')

I have endomags and also a Colt mag setup. I recently bought the Stern Defense glock 17 mag adapter to try w/ my CMMG RDB 9mm upper. I removed the ejector and LRBHO features as they aren't needed and interfere w/ the RDB bolt. I've read some folks say this setup works. My problem is:
1) The Stern adapter rubs the bolt carrier. The little ear that supported the LRBHO feature is sort of in the way. If I know this setup will work, I'll just cut it off, clearance the bolt carrier slightly, or mod the Stern adapter to sit a little lower.
2) The G17 mags sit too high and the bolt lugs hit them. Is this related to #1?? Is the whole adapter sitting too high or just the mag? Using a real Austrian Glock 17 mag. I could just file the inside of the ears on the mag and it would work but I'm wondering if this is 'normal' or something was incorrectly machined on the adapter.

I took some pics.
Pic 1: The shot from the right side of the lower, you can see the LRBHO tab that sticks up (has a little hole in it.) Thats problem #1. Not a big deal right now. The rear of the mag is just forward of this point and about the same height.
Pic 2: I measured 10mm from the top rear of the mag lips down to the receiver. That's how far the back of the mag sticks out of the lower.
pic 3: bolt to mag lip contact. This is problem #2 above. The two bolt lugs will actually fit between the glock feed lips but the back of the mag is a little narrower and the bolt catches it.

Can anyone shed light on this? Or make the same height measurement if you have either a Stern adapter or a dedicated Glock mag lower that you use w/ a RDB BCG? How far are the mags supposed to stick up?

 

[teratos]

I have a Colt mag lower working with a RDB bolt/barrel. I had to do a lot of Dremel work on the feed ramp and cut the mag catch down so the mag sits lower. Not sure if that helps

 

[smdub]

Dr T, We had to do the same w/ the Colt adapters. Its working but I hate that darn adapter. I modded my top insert adapter to drop in w/o having to take the LRBHO out. So at least its quick to drop in. Edit: Matt uses a bottom insert Uzi (basically Colt) adapter. It sometimes drops the adapter out when he uses the AR mag drop. We don't like the different manual of arms when using the adapters.

My endomags mostly work. I bought a bunch of magpul G2 mags at the PA show in FDE so I can tell them apart. Matt's endomags are far less reliable. Online reviews of them are definitely hit/miss.

So I'm trying the Glock mags. The Aero EPC upper has a clever way to actuate the AR15s stock LRBHO. It rubs the Stern adapter slightly but I can fix that. If I can get the Glock mags running reliably I'm going to 3d print adapters for them to basically make them dedicated 'black dog like' AR15/9 mags. Run w/o the Stern adapter. But need to walk before I can run...

 

[smdub]

Is there a problem here?

CMMG innards with an MP5 mag accepting lower. Best of all worlds. Zero failures. SIG brace, optional...

Yes. Its not available w/ a transferable full-auto M16 lower. That's why we aren't running a dedicated Colt/Glock/HK mag lower.

 

[outrider58]

Yes. Its not available w/ a transferable full-auto M16 lower. That's why we aren't running a dedicated Colt/Glock/HK mag lower.

Ah. I did not realize we were talking about FA.

 

[smdub]

I've been searching a lot today trying to figure this out I'm seeing more reports of people having to modify the Stern to sit lower. I somehow missed all of those before I ordered

Plus, looks like someone here has had a similar problem in 45 w/ their RDB:

Looking for Advice; this CMMG RDB Setup Does Seem Compatible with my Lower

I built this AR45 (45 APC braced pistol) using a New Frontier lower (branded as Spartan for Joe Bob Outfitters). It uses the new Frontier upper and lower, plus a CMMG Radial Delayed Blowback with an 8" barrel. I removed the ejector on the New Frontier lower. So I am trying to adjust the last...

www.mdshooters.com

They made a good observation I hadn't even gotten to yet. After the last round, the rear of the bolt will catch the mag follower sticking up. Ugh. Looks like I'm going to have that problem too in 9mm. Time to rethink this Glock mag idea then...

 

[gmharle]

Will the set screw in the bottom of the Stern adapter not give you enough adjustability to sit low enough? I have one with just a straight blowback (not CMMG radial) and use the last round with a dedicated 9mm Spikes Glock lower. They do have a note on the website stating that you need to use a glock cut bolt. I have a Faxon bolt in mine. Video explanation here.

 

[smdub]

No, the setscrews just pull it tight against the mag catch. They can't set the height (the mag catch does that.) I'm thinking about raising them up enough (which would prevent the adapter from locking into the magwell) and just holding it in by hand and trying to shoot it. I think the bolt/mag follower issue is still going to be a showstopper.

I also have a Torkmag Maddapt 17 adapter on order (it was cheap at $60.) Was planning to cut off the ejector and try it w/ the RDB. It will have the same follow/bolt interaction though so my hopes are dashed before I even got started.

 

[Bountied]

Endomag has a different version that doesn't have the ejector. Their website discusses CMMG RBDs and you need the ejectorless version. I use those in my RDB with a standard lower and it works flawlessly. Have you seen/tried those?

 

[smdub]

We all have the ejectorless endomag versions. The RDB bolt won't even chamber a round w/ the integrated ejector version.

 

[GuitarmanNick]

I have used EndoMags with good results, but switched to a Stern Defense adapter to work with Glock mags.

Neither system had any problems like you are experiencing. My build is direct blowback and has a hybrid cut(works with Glock or Colt style mags) BCG. I am unfamiliar with the CMMG system, but as gmharl mentioned above, maybe an incompatible BCG is the cause.

 

[Bountied]

We all have the ejectorless endomag versions. The RDB bolt won't even chamber a round w/ the integrated ejector version.

I saw you are using Gen2 Magpul mags? Have you tried Gen 3 or higher? I've had zero issues with my RDB and endomags in Gen3 Magpul mags.

 

[smdub]

I have used EndoMags with good results, but switched to a Stern Defense adapter to work with Glock mags.

Neither system had any problems like you are experiencing. My build is direct blowback and has a hybrid cut(works with Glock or Colt style mags) BCG. I am unfamiliar with the CMMG system, but as gmharl mentioned above, maybe an incompatible BCG is the cause.

Blowback systems don't have these mag issues. But a delayed system is soo much smoother shooting and less gas to the face thus the appeal to try to get one running perfectly.
Can you please measure how high up a glock mag sits in your Stern adapter? Maybe just a pic from the right side like my first one? If the back of your mag also sits as high as the LRBHO tab then my adapter isn't abnormal.

I saw you are using Gen2 Magpul mags? Have you tried Gen 3 or higher? I've had zero issues with my RDB and endomags in Gen3 Magpul mags.

Thats an interesting point. I don't recall exactly what magpul mag bodies I had the endomag inserts in but I went down to the mag drawer and all the ones in the front were Gen2 so it had to be them. Again, mine seemed to be mostly reliable. I just noticed the new FDE magpul bodies I just picked up to put the endomag inserts in are Gen3. So if they start acting up I'll switch back

We're getting off topic as I really just want to know about Glock mags and/or the Stern adapter. But while we are talking endomags...

I've now had the sales VP of Mean Arms (endomag) call me twice out of the blue to respond to emails I've sent them. (last one was just yesterday) I have one of their new bearing delayed uppers on preorder (its stupid expensive and I'm still not sure I'll go through w/ the buy.) I'd *REALLY* like to just be able to buy the bolt/barrel combo and not all the other junk but thats a story for a different day. I have found out that Mean Arms parent company is a very large injection molding company. For the life of me I can't figure out why they made a magpul mag insert vs just designing a complete mag to begin with! Why tie yourself to some other companies tolerances, versions, etc when you have the capability to do it all from the get go? I have asked them this question directly and don't get an answer. I really did appreciate being able to have a real conversation with them and liked that they reached out to me, but since they don't respond via email its basically a sales guy doing a sales guy pitch. They pretty much sidestepped answering any of my very carefully thought out and drafted questions/concerns.

 

[Bountied]

Blowback systems don't have these mag issues. But a delayed system is soo much smoother shooting and less gas to the face thus the appeal to try to get one running perfectly.
Can you please measure how high up a glock mag sits in your Stern adapter? Maybe just a pic from the right side like my first one? If the back of your mag also sits as high as the LRBHO tab then my adapter isn't abnormal.


Thats an interesting point. I don't recall exactly what magpul mag bodies I had the endomag inserts in but I went down to the mag drawer and all the ones in the front were Gen2 so it had to be them. Again, mine seemed to be mostly reliable. I just noticed the new FDE magpul bodies I just picked up to put the endomag inserts in are Gen3. So if they start acting up I'll switch back

We're getting off topic as I really just want to know about Glock mags and/or the Stern adapter. But while we are talking endomags...

I've now had the sales VP of Mean Arms (endomag) call me twice out of the blue to respond to emails I've sent them. (last one was just yesterday) I have one of their new bearing delayed uppers on preorder (its stupid expensive and I'm still not sure I'll go through w/ the buy.) I'd *REALLY* like to just be able to buy the bolt/barrel combo and not all the other junk but thats a story for a different day. I have found out that Mean Arms parent company is a very large injection molding company. For the life of me I can't figure out why they made a magpul mag insert vs just designing a complete mag to begin with! Why tie yourself to some other companies tolerances, versions, etc when you have the capability to do it all from the get go? I have asked them this question directly and don't get an answer. I really did appreciate being able to have a real conversation with them and liked that they reached out to me, but since they don't respond via email its basically a sales guy doing a sales guy pitch. They pretty much sidestepped answering any of my very carefully thought out and drafted questions/concerns.

I was just trying to trouble shoot one of the options you had trouble with. I don't have the Stern adapter, sorry no help I know.

If the endomags pretty much work have you tried adjusting your buffer or buffer spring? What kid of failures are you getting in full auto with the endomags? Double feeds, failure to feed, failure to eject, stove pipe etc.?

 

[GuitarmanNick]

Here are a couple of pics of a Glock mag locked into the adapter.

Looks about the same to me. Yours may be slightly higher.

What type of BCG cut do you have. Sounds like it is not cut right for the mags you want to use if it is hitting the adapter.

 

[smdub]

Thanks! Yeah, yours looks roughly about the same.

 

[gmharle]

Thanks! Yeah, yours looks roughly about the same.

Mine looks about the same.

 

[gmharle]

No, the setscrews just pull it tight against the mag catch. They can't set the height (the mag catch does that.) I'm thinking about raising them up enough (which would prevent the adapter from locking into the magwell) and just holding it in by hand and trying to shoot it. I think the bolt/mag follower issue is still going to be a showstopper.

I also have a Torkmag Maddapt 17 adapter on order (it was cheap at $60.) Was planning to cut off the ejector and try it w/ the RDB. It will have the same follow/bolt interaction though so my hopes are dashed before I even got started.

I agree that they pull it down against the mag catch for spacing but, the center screw is what actually tightens the wedge that holds it in place and keeps it tight. I don't think that you need to be on the mag catch to hold it in. I can set it to be flush with the top of the receiver. Or you could even file the ledge that the mag catch rests on for that matter. Of course the LRBHO won't work but you don't want that anyway. I think that I would adjust it and tighten it that way before I just held it in place by hand.

 

[smdub]

I agree that they pull it down against the mag catch for spacing but, the center screw is what actually tightens the wedge that holds it in place and keeps it tight. I don't think that you need to be on the mag catch to hold it in. I can set it to be flush with the top of the receiver.

Good idea! I did this and can confirm it will chamber and fire rounds w/o hanging on the tip of the mag follower.
If it insert it just enough to clear the Stern LRBHO tab I can't insert a loaded mag on a closed bolt. Just a little lower I can and it still appears to feed ok.
Looks like the Stern could be permanently modified then to work (mill mag catch lower and cut off the LRBHO tab.) Not sure I'm ready to go that far though yet.

The Torkmag Magadapt 17 came in today. I need to trim a mag for the AR bolt catch using its template to do some testing.