I have built several 5.56 ARs and can’t get them as compact as I’d like as I can’t bring myself to go under 10.5” barrel and have an SBA3 brace.
I’m hoping to build a “little” AR9 with the following specs/questions:

Would like a 5” barrel and small blast can that fits almost completely under the handguard.
I think I would like to go with an old-school pistol buffer tube as it is more compact but may add a small brace if there is a decent compact one.
This will most likely be an open sight only gun, maybe I’d put a super compact red dot on there but I have an astigmatism and only the circle dot type is remotely clear to me and super compact dots seem to just be 4 MOA dots.
In a perfect world I’d like a build without a buffer tube but most likely that would require a very expensive upper.
I have a spare standard lower laying around, should I use that with a mag block or get a AR9 lower?
I shoot mostly compact pistols and revolvers and my only full size is an M&P.  So I don’t know whether to go Glock or Colt or CZ Mags…
Don’t care too much about last shot hold open.
Would love a side charger.

I’m trying to keep this as compact as possible.  Would I be better off going with an off-the-shelf option?
The best looking upper I found so far is this 22-Mods-For-All 5.5" Stinger:



This woudld be $270 for the complete upper and I'd have to find a mag block and finish out my lower.  I could probably be all in for about $500 with my current lower.  I can get a full AR9 complete pistol from PSA for $550...

I have 1 side charging 9.5" 300 BO. While the side charging is cool, I won't spend that $150 ~ $200 premium again. I would spend it elsewhere. Plus almost all side chargers are heavier billet. Phase 5 makes some nice pistol buffer tubes if you don't want a brace.

I am running Colt style mags using a I believe Daytona Tactical mag block. I am using a Tubbs flatwire AR 10 spring and a Taccom multi stage buffer (Link here). and mine runs 100% reliable. Only trouble I have determined I have a defective barrel and am waiting the manufacturer to test and replace I hope. It patterns like a shotgun.

If you really plan on iron sights I would go with a carry handle and Troy HK style fixed front sight with a Blitzkrieg sight.



Edit that's a "chopped" rear sight.
I regret not doing it carry handle. Now I've re arranged all again though. These things are just dress up Barbie Dolls for men.

You can always go with the Mean Arms EndoMag setup in your standard lower since it sounds like you would have to buy 9mm mags anyway.  Could be a cheaper solution as long as you have extra P-Mags laying around.

https://www.meanarms.com/products/detail/endomag-9mm

I am in the process of building my second 9mm AR using EndoMags.

IMO if you are going for compact, get a 4" handguard to use a 5.5" barrel.  I personally do not like the handguard over the flash can setup.  I wanted as short as I could get.

I will echo the others in saying that the endo mags would be an easy way to use a standard Ar15 lower with 9mm upper.  Order through a vender like AIM surplus and get free shipping on a 3 pack.  I did 2 9mm builds and used Colt and Glock mag PSA lowers.  At the time, PSA had some good deals on the Metalform Colt style mags.  Glock mags are still fairly cheap and easy to get (ETS and Magpul mags as an example)

My 5.5"9mm PSA Colt lower:

Aero Precision should start selling their new dedicated 9mm receivers, next month. I'm probably going to use those.

https://www.youtube.com/watch?v=9sBSkJOFdKg

Can we get the complete build specs on this looks great!

Pardon my ignorance but wouldn't it be cheaper to just go with a dedicated 9mm lower, instead of buying four or five of those adapters?

Yes and No.  The cost of a cheap lower for me is $60 with FFL fee ($40 lower, about $8 shipping, $10 fee).  Add a LPK and a brace kit (complete with buffer tube, buffer, and spring) to make it a pistol and you're into it approx $170ish.

Endo mags 3 pack from AIM Surplus is $80 with free shipping.

With the endomag you an use any of your 5.56 pistol or SBR lowers and all you need is a 9mm buffer to drop into the lower.  I have been debating buying two 3packs and selling a single.  5 mags should be fine.... and even if you have 6 it's still cheaper than building a dedicated lower.

I just finished a 4.5" barrel pistol, used a Stern Defense lower block, Stern Defense BCG, faxon barrel and the rail and upper I had. I found the Stern Defense block on ebay for $140 NIB. Took it to the range last weekend and it worked perfect not even a hiccup. I used a 6.4oz 9mm buffer with standard carbine spring.

Joeboboutfitters is currently running a sale on a non-LRHO Spikes 9MM upper for $104. That'll save you some money, but there's really not that many places you can trim using new parts.

All my builds use the LRHO version of this upper except for my RDB. Joebob and Stern Defense (getstern.com) supplied just about every part I needed.

I ended up with a Phase 5 pistol tube (I normally just run this, but the SBA "mini" pistol brace works fine with the P5 and is as small as they make them -- and it's also their cheapest.)

I strongly advise going with a dedicated lower, Glock or Colt depending on preference and if you already have glock 9mms.

ETA: My builds use Stern's 4 inch handguard. This lets you use a 4-4.5 inch barrel and a much shorter muzzle device (if any). That lops 3-4 inches from the overall length of the pistol and makes it much more compact.

I also used the 22 mods for all 5.5 stinger upper. Cost wise I got in on one of the Anderson lowers for $29. BLR for a lower kit, $30 or so used pistol buffer tube and spring $10 and Ebay pistol brace $12. Got 5.5 oz buffer $25. So for around $100 or so have a complete lower. I then found a ProMag adapter for Colt style mags for $60. Still under $175 and a complete ready to fire lower. Found adapter really likes ProMag mags 32 round steel reinforced polymer for $12 each, bought 4. So far I've run 300+ rounds through it with only one jam at the end of a mag. Runs well and at 25-50 yards and a cheap red dot very accurate. Takes the 10 ring out of the target with 30 rounds. Would buy from 22 mods for all again even though not very well known. Everything I have bought from them has functioned well and the one issue I had was corrected instantly by them. I originally built this using a FMK Poly lower but it badly cracked so replaced it with the Anderson and haven't looked back.

I did this one with a budget upper from Primary Arms and a standard lower with endomags. So far it has been flawless. Attached File

not an answer to your question (I'm in the process of converting a PSA billet Glock AR with a LAW folder myself) but you might look at the new Ruger 9mm PC Charger... with a folding brace and no receiver extension (buffer tube)... its a couple of hundred more... just a thought


https://www.youtube.com/watch?v=BWU5Xo6jwtM

I've built a few with glock and Colt pattern/modded Uzi mags. IMHO the Colt/Uzi mags are better because the mags are inserted straight vs Glock mags which are inserted at an angle. Also the LRBHO is good for continuity of training with your standard AR. I built a pistol with a  5.5" Foxtrot Mike 5.5" barrel 79.00, Spikes buffer tube spacer 20.00, Anderson upper 34.00, KAK slim blast can 20.00, KAK BCG 99.00 and KAK 9mm mag adapter 89.00. All this dropped on a standard AR pistol lower with a carbine buffer, tube, spring and it runs like a little sewing machine. If you want a complete 9mm pistol upper I'd go with the PSA or a Foxtrot Mike complete pistol upper with BCG on sale at PA for 349.00