Yep, more experiments and busting of myths.

I built a 9mm AR takedown upper without doing anything special, no tools, and the one "necessary" part for this to work is an el-cheapo $20 handguard, and it works fantastic.

I've been using an upper for experiments for a while now where I switch the barrel often.  Taking queues from the Henry AR-7 takedown, I just used a traditional spikey AR barrel nut, hand-tightened to hold the barrel on. You may see it in my videos now and again.  And... It works just fine!  No need to torque the barrel nut "to spec".

From there I decided to see what handguard/barrel nut combos were available to make it more "official", and found the Presma tubular handguards. These are the simplest of handguards - just a tube and a round barrel nut.  By attaching the barrel nut (with red Loctite) to the handguard, the whole assembly becomes a big takedown barrel nut. As long as the handguard/nut stays tight during use, it runs just like any 9mm AR (and just like any screw-on barrel nut takedown gun).  It may not be pretty or "sexy" like an M-LOK handguard, but it works just fine.

As a bonus - this can be assembled as a completely tool-less 9mm upper (build list/prices in article below).  It requires no vice, no vice block, no torque wrench, and no crows-foot wrench to assemble. Red Loctite or other semi-permanent thread locker for attaching the barrel nut to the handguard (NOT the receiver) is strongly recommended.  The barrel nut assembly just needs to be monitored to make sure it remains tight.  In practical use, I've never had it loosen by itself as long as I gave it a good final twist during assembly.

All the details: https://blowback9.wordpress.com/2024/05/16/takedown-9mm-ar/

Direct link to the video: https://youtu.be/j_OuND6VngU

Regarding torquing the barrel nut to spec, because this is ARFCOM, home of the armchair expert and the not so tongue-in-cheek "You're going to blow your hand off, kid." boomer comments...

As far as every reference I can find says, the recommended barrel nut torque spec for the AR platform was intended to keep the handguard from rotating due to heat and vibration from the high pressure rifle cartridges. Handguard/barrel nut rotation could impinge on the gas tube and potentially cause accuracy and headspace/lockup problems.  For a lower pressure simple blowback 9mm pistol cartridge AR with a tubular non-oriented handguard and no gas tube, as long as the barrel remains firmly against the receiver it seems to work just fine, just like any other takedown gun.

ETA: I make NO income from any of this (although I do welcome Buy Me A Coffee donation gifts through my site) and I am NOT paid any money by any company.  It's my "retirement hobby" and that's it.

Two thumbs up to you, sir!!!

I've been running a 9mm upper just like that for at least 30 years now.  This was put together back when tubular handguards were the only free-float handguards available.  Give the handguard a good twist when assembling and it's never loosened up.

If you are handy, you can come up with a ratcheting/detent system for this. I have a few ideas for it.

Like:

-On a 9mm/22 upper drill a channel into where the gas tube would normally go.
-Use a spring and detent system similar to what an AKM uses for the front sight/muzzle device. Just enough so the detent can be pushed back in via rotation, but won't come loose during firing.
-Cross pin the detent and spring so they don't fly out.

With uppers being pretty cheap now, it might be worth it for an experiment.