Since I had a couple of SBR'd AR15 lowers sitting in my safe doing nothing, it seemed about time to convert one of them to a 9mm AR.

So, here it is:



I've built dozens of ARs so I felt comfortable installing the top-loading Hahn 9mm conversion block - the one that locks back on Colt mags with a standard bolt catch. The rest of the parts include:

- Spinta blem ramped 9mm BCG
- Ballistic Advantage 11" barrel (same external dimensions as an AR15 10.5" barrel) threaded 1/2x36
- New Frontier Armory A2 FH
- MI Gen3 KeyMod 9.25" handguard
- CMMG ejection port conversion kit
- CMMG heavy 9mm buffer (5.6oz)
- New Frontier Armory 9mm buffer spacer (leaves about 1/4" between the bolt fully back and the bolt catch)
- Vortex SPARC AR
- Brownell's Colt-pattern 32-round mags

The Hahn block is expensive, but boy is it well-built. It would not fit into my Mega SBR lower (too tight) but slid right into my LMT lower (hooray milspec). I can push-pull fully loaded mags with no issues, and mags drop free. I did have to replace the notched LMT hammer with a smooth one from my M&P15 lower, but that took all of three minutes.

Also, I have a Norgon ambi mag catch installed and it works just fine.

Hand cycling reveals no problems. Very much looking forward to shooting a bunch of mags through this one in the next couple of days.

Future plans include an Omega 9K and cases of 9mm... Hopefully I won't have to buy a dozen bolt catches, too.

Standard carbine spring, but I have a Tubbs flat wire spring just in case. I've build a whole bunch of ARs so I have a whole bunch of odd parts...

Quick Range Report

I had a bit of time this morning so I went to my gun club and put 3 32-round mags through the 9mm build. I used Prvi 115gr brass-cased ammo.

Overall, things went well.

Recoil was "rubbery" when compared to the crisper "slap" of a 5.56 rifle, probably due to the buffer bottoming out on the rubber stopper in the receiver extension. The bolt locked back on empty mags and the bolt catch did not break.

The first mag fed with no issues. I had one FTF each in mags 2 and 3. Here are a couple of photos of one of the rounds that FTF'd:




As you can see, the bullet hung up on something and experienced set-back and a damaged tip. I'm guessing a heavier buffer will solve this issue by slowing the bolt down.

Accuracy was fine. The green area below is my final 6 shots to confirm zero at 50 yards. The blue area contains a full mag fired at a fairly rapid pace, maybe 2 rounds per second or so. The barrel and Vortex SPARC AR are fully capable of great accuracy, so I'm happy about that. Obviously, I need to work on my technique.

Very nice looking build!

It seems many have a little problem getting their 9mm builds to run right at first, or some ammo doesn't run well. I was lucky. I have over 1K rounds suppressed and unsuppressed through mine with all kinds of different ammo, and not a single hiccup. I like it so much more than I thought I would. Suppressed it makes a nice home defense gun. Slap on a flashlight and a red dot and you are good to go. Anyone who thinks it is a good idea to use a 223 AR for home defense is crazy. Touching off a 223 indoors is very disorienting, not to mention the hearing damage, both instant and permanent. A suppressed 9mm SBR with 30 rounds is good for me. If I am expecting a horde of Zombies, or a football team on bath salts I'll grab my 300BLK AR with 220gr expanding subs or Barnes TSX 110gr supers.

Hey thanks!

It took me a bit to get used to the rainbow trajectory of the 9mm bullets - when shooting 5.56 I don't see any meaningful difference in POI between 50 and 75 yards, but with 9mm the difference is obvious. I'm really looking forward to getting this build settled down then shooting a bunch of ammo at the pistol-only plates at my club.

Yeah, as with any pistol caliber carbine, I really think of a 9mm AR as a 50 yard gun or a home defense gun. Especially an SBR 9mm AR with a short barrel. It is not going to perform much different from full-sized a 9mm pistol. I just wouldn't bother with it over 50 yards.

That's interesting. I had not considered a 25yr zero. I will try that next time I'm at the club.




It was doing pretty well against the steel plate hanging at 75yds...  But you're right, this build is for close-in stuff.

I have a Tubb AR15 flat wire spring installed now along with the CMMG 5.6oz buffer and the New Frontier buffer stop. I'll see if this combo cures my sporadic FTF issues.