The AR-9 Super Lower V1.0

You asked for it. And it has arrived. I released the V1.0 AR-9 Super Lower a few days ago. Here are the details.

My goal for the project was to have a 9 MM lower that would work with Glock magazines, use as many standard AR-15 parts as possible, and feature a last round bolt hold open. I have met two of those goals so far. The last round bolt hold open still remains elusive.

The V1.0 AR-9 is basically a V3.0 Super AR-15 Lower with a redesigned front end. The front pin plates on the AR-9 are the same as on the AR-15.

The only non AR-15 parts in this AR-9 lower that can not be 3D printed are, the 3/32″ roll pin used to secure the mag catch lever, and the heavy buffer needed for reliable operation.

If you want to buy all the parts you need to complete the AR-9 lower, all you will need is this pin, an AR-15 Combo Kit, and the KAK heavy 9 MM buffer.

Both the magazine catch and ejector are 3D printed. Yes, you read that right, the ejector is also 3D printed! This saves us the trouble of having to source a third party ejector.

The ejector is 3D printed separately and simply presses into the lower body. The edge of the upper is what holds the ejector in place. It is as secure as screwing it in, but without needing any fasteners.

I have had some concern as to the longevity of this plastic ejector, since almost all other ejectors are made from steel. But so far the Overture Easy Nylon ejector, after more then two hundred rounds of 9mm, shows no signs of wearing out!

To date I have fired 224 rounds of 115 Grain FMJ ammunition without a single failure or malfunction! It took awhile getting here though! Below can be seen some of the prototypes that where needed to get all the right parts into the right places. The magazine position proved to be critical for proper feeding.

I assembled the upper using a KAK AR-9 Bolt and Barrel. The upper is a simple mil-spec stripped upper. I found it very important to use the right buffer mass, My first test ended with a case separation that I believe was partly caused by a light carbine buffer. I am now using a KAK heavy extended AR-9 buffer.

Here you can see the aftermath of the case separation. Fortunately the lower was the only part harmed by the accident. The overly light buffer allowed the bolt to open too quickly while there was still tremendous pressure in the shell casing. Once the shell was no longer supported by the chamber walls, it ruptured under the force. I have not had a single problem since moving to the heavy eight ounce buffer.

The mag catch is 3D printed and attaches to the lower using the steel roll pin. It is powered by the very same spring that powers the AR-15 mag catch. Which is very convenient.

Here you can see the print orientation of the two small parts. I think that a Nylon is perfect for the ejector. As Nylons have excellent wear resistance. However, the Nylon mag catch on my latest AR-9 print has bent out under the continuous force of the spring. It still works, but I think a Carbon Fiber Nylon or Polycarbonate would be a better option.

So you want to print one? First you will need to head over to the Downloads page and grab the files. Then you will have to source the parts. I will start selling complete AR-9 Combo Kits once I get all of the parts. But for now you will have to order a few different items. In addition to the AR-15 Combo Kit you will need a 3/32″ x 1″ roll pin and a heavy buffer. I recommend the KAK extended 9 MM buffer :

For the upper you have lots of option, But I, once again, recommend KAK equipment.

This is the bolt I use:

And here is the barrel: You can of course use other barrel lengths.

Any AR-15 stripped upper and handguard will work with the above equipment.

Below I have imbedded my latest video testing the AR-9 lower.

That’s all for today!!

23 thoughts on “The AR-9 Super Lower V1.0”

  1. Great Job on this. If you are looking to implement last round bolt hold open, I think the only reliable way with a printed lower is to do an external connection like the foxtrot mike configuration.

    I have printed many of your lowers and I always edit the step files to include cutouts between the fcg pins so I can put Anti-walk pins and hardware in. This is the only lower that I’ve had issues with so far; I ran a couple of file checks on it and it looks like the outer wall (only on the left side of the lower) is open in some way; most likely a bad export or something from Solidworks. I haven’t been able to find where the issue is yet though so I will wait for a v1.1+ update or something before I can make my usual edits.

    I also like extra features near the pistol grip mount.


    1. I found the open face from the step file. There are two curved faces between the buffer tower and the pistol grip mount on the rear and it appears they aren’t stitched together somehow.

    2. I’ll have to fix the STEP file! As to the LRBHO, I like the way FTM does it, but they are using a custom BHO lever. I want to use the Mil-spec lever, if possible.

    3. LRBHO can also be acheived in the upper receiver. Aero EPC-9 & Spartan Uppers have LRBHO built into the upper receiver. They work flawlessly.

  2. I’m very excited to see this release. Is it compatible with Foxtrot Mike uppers, due to their specific wider geometry??

  3. The “Let’s Go Brandon!” easter egg of sorts made my day. Immediately sealed the deal on which lower I am printing first.

  4. First I absolutely love your designs and the way you explain everything. I’m really looking forward to building a few of your designs to add to my collection. But I dont want to chance screwing it up so here’s my question and Maybe I missed it and if so sorry but I’m looking through your list of stuff I need to buy in order to build this and I don’t see which upper I need to buy other than that I “have lots of options”. Specifically I would like to know do I need an AR15 upper or a AR9 upper. Do I need a stripped upper or complete upper and will a complete AR9 upper work with this lower? I’ve done several handguns but your AR15 and AR9 will be my first AR gun builds and really want to get it right. sorry again about what I’m assuming are noob questions. Thank you!

  5. I was excited to give this a try. I’m using a PSA upper, barrel, and BCG.

    It printed and assembled just fine but I am having feeding issues. The bullets impact the chamber face about a millimeter too low. If I push the magazine up (above the mag release) about that millimeter it will feed but this obviously can’t be maintained. Does the KAK barrel you are using have a feed ramp? Or did I perhaps misprint the lower?

    Any insight would be appreciated.


    1. I am having the exact same issue with the exact same parts(PSA). What material did you print with? Did you adjust anything from Tim’s recommendations. I was thinking about either adding a feed ramp(not sure how) or adjusting my print settings somehow. I’m using eSun PLA+ and other than the feed issues(~20-40% of the time it runs flawlessly).

      1. I typically use Tough PLA or PLA+. It’s worked great for the 5.56 lowers so I don’t think that’s it. I don’t change any of the print settings either. I’m struggling to figure the best way to insert a feed ramp. I think just adding it to the print would create a very high wear surface when the case lip slides over the poly ramp. I’ve considered, just as a experiment, driving in a carpet tack or even a small hex screw into the lower ahead of the magwell and then using a dremel to shape a ramp for more wear resistance. I also noticed that if I raise the magazine a millimeter or 2 above the mag catch that it will feed so moving the location of the mag release might also fix the issue but that would involve modifying the basic CAD file.

      2. With some time to think and a bit of sandpaper, I resolved the feeding issues. Looking at the juncture of the upper and lower receivers at the forward end, I saw a bit of a gap. So I took the lower off and loosened the two small bolts holding the twin take-down pin plates in place. There is a bit of slack here to allow for slight variations in dimensions of the lower. I noticed that there was a bit of flashing around the bottom of the plates and sanded that smooth, maybe even taking off a bit more, and then reassembled. I made sure to push those plates down towards the lower surface of the lower as tight as I could.
        I filled a mag with 9mm snap caps (always a handy thing to have around) and they fed just fine. I did this several times with several different mags and the problem seems to have cleared up.


        1. After reading your other post about modifying the take down pin plates though I think that actually sounds like the correct way to address the overall feeding problem and I will be trying that very soon. I had to put more pressure than I like on the take down pins to fully insert them and I noticed that there is still a very slight gap between them so I think I will change tactics and address that first before trying the modified mag catch. I am curious though, you mentioned snap caps but have you tested it with live ammo? I’m thinking the difference in forces applied to the lower during live fire vs hand racking might be enough that more testing may be needed to know whether its actually fixed? I’d love to hear more about your experiences.

  6. Will this work with a CMMG Radial Delayed Blowback upper including LRBHO functionality by chance?

  7. You’re idea to insert a small piece of metal that you custom shape to fit as a psuedo feed ramp is interesting, I might have to look into that. Like you, I also discovered that if I put upward pressure on the magazine that my experience was much improved though I didn’t have to go so far as actually depressing the mag catch. On my part I did end up taking the Mag catch in FreeCad and modifying it to make the actual catch part higher but I haven’t had a chance to test it yet to see if it actually helps.

  8. Tim, I was one of those folks having feeding issues with the V1.0 AR-9 lower. I downloaded and printed the V1.2 when it became available but just today I had a chance to take it to the range and try it out. It worked flawlessly! I put more than a hundred rounds through it without a single feeding or extraction issue. You were spot on about the magazines too. Glock OEM and MagPull mags ran just fine and fell free when empty but a couple of no name generics wouldn’t even insert much less feed or drop free.

    Really nice work on this, thanks.


  9. Just out of curiosity, what style ejector is used just in case I want to replace it with a metal one?

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