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The 21st Century Frontier Carbine

By Lawrence Hansen

Three topics are guaranteed to start an argument, even among civilized people: politics, religion, and whether or not the AR- 15’s 5.56/.223 chambering is adequate for anything more ambitious than varmint hunting. Sometimes a consensus can be achieved - until somebody lobs a grenade into the fray and, say, extols the virtues of an AR in 9mm Luger.

WHY A PISTOL-CALIBER AR?

The same logic our frontier ancestors used in having their Winchester (or Marlin) saddle carbine chambered for the same round as their Colt Single Action Army (or Smith & Wesson Model 3 Schofield) is still valid. It simplifies your supply logistics, while equipping you with a gun that can reach out a lot farther, and more accurately, than your sidearm. No, you won’t be able to drop a mule deer at 1,000 yards, but your “AR-9” carbine will be plenty effective at ranges beyond arms-length. The heavier 115 to 147 grain bullet is also less likely to over-penetrate than the .223, and you can punch up the self-defense effectiveness with hollow point ammo.

How much punch does a 9mm pack? JP Enterprises says its GMR-13 carbine delivers ballistics comparable to a .357 Magnum, with 3 MOA accuracy at 100 yards. The 9mm produces less muzzle blast, making it helpful in training novice shooters, as well as a good choice for use in enclosed spaces like buildings.

The ammo is inexpensive, plentiful, and easy to reload in enormous quantities on a progressive press. It won’t tear up steel targets in 3-Gun competition, yet is still as accurate as .223. Unlike the full-on rifle, a 9mm can be used at many indoor ranges, making it great for wintertime training for those of us who live in rainy/snowy/cold climates.

It is also very quiet when shooting subsonic 147 grain ammo with a sound suppressor. Suppressors just became legal here in Iowa earlier this year, so we now have a new option for potent, silent coyote medicine! Make nice with NFA regulations, install a short barrel and a suppressor, and you have the civilian, semi-auto equivalent of the Colt SMG - suh-WEET!

But the biggest reason for having a 9mm AR? It’s so fun to shoot! It gives you cheap plinking fun with a round that makes a way bigger bang than a .22. Now that I’ve convinced you the AR-9 is a sensible, realistic, necessary addition to your collection, how do you get one?

OFF THE SHELF OR DIY?

Several manufacturers offer dedicated, built-from-the-ground-up 9mm AR-15 rifles, so that’s the easiest option for getting one. I don’t have empirical data to back this up, but I suspect that the majority of AR-9s start life as a spare standard 5.56 rifle that’s been superseded by something newer, cooler, and better equipped. One day, the owner spies the forlorn safe queen and starts thinking about a project... Several key component changes later, and that ordinary, work-aday AR-15 is transformed into a fun-shooting 9mm carbine.

LOWER DEPTHS

Since the 9mm Luger cartridge is distinctly shorter than the .223/5.56 and most AR-9s use a modified submachinegun stick magazine, we need to fill up the extra, front-to-back space in the magwell. Some companies like JP Enterprises and CMMG offer dedicated 9mm lowers with the magwell opening neatly machined to the exact size. These receivers will cost some extra coin, but they are by far the slickest, neatest-looking option.

The JP comes with an ambidextrous mag release, bolt release, and ejector already installed and a nice, integral triggerguard machined right into the receiver. But the most unique part about it is that it uses Glock® 17 pistol mags, especially the handy 33-rounder (#100- 002-771), so if your sidearm of choice is a 9mm Glock, this gives you another soupçon of commonality with your carbine.

A bit more on magazines. Most AR-9s use stick mags designed for the Colt and Uzi subguns. We are partial to our own Brownells-brand 32-round mags; they’re all-steel and built to hold up.

If you’re repurposing a standard lower, you’ll need a conversion block - an insert that fills the gap and correctly retains the tall skinny mag - such as those from Hahn Precision, Pro Mag, and Rock River Arms.

Because the AR-9 fires a cartridge with entirely different ballistic characteristics from AR-15’s .223/5.56 and it uses a different bolt/carrier setup (more on that in a minute), it requires a different buffer and spring. Some 9mm BCGs also require a different hammer, while others work with the standard AR-15 hammer. The good news? Yup, we carry all of those, from Rock River Arms and others. What your particular lower needs will depend on the configuration of your chosen upper.

UPPER REACHES

As with the lower, you can get a complete, dedicated 9mm upper ready to plug-n-play, from well-respected names in the AR-15 world like CMMG, Rock River Arms, and Yankee Hill. But you can also start out with a stripped AR-15 upper; a good-quality base model like the Aero Precision works just fine. If you go that route, you’ll need a barrel, such as one from Brownells, CMMG, or Yankee Hill. But since these guns operate on a simple blowback system, you don’t need a gas block and gas tube.

The last major piece of the puzzle is the bolt/carrier group. Actually, it’s not so much a “group” as a heavyish “blob” because AR-9s employ simple blowback operation and the bolt is not separate from the carrier. One thing to watch for: some BCGs require a different hammer from the standard AR-15 hammer. Others, like the CMMG “Enhanced” 9mm BCG have a ramp cut into the bottom to provide clearance for the factory .223/5.56 hammer, making for easier conversion back to a standard AR.

WRAPPING IT UP

If you’re doing the most elaborate conversion possible from stripped standard receivers, the toughest chore is installing the barrel and, if required, changing the hammer. The rest requires skills not much more elaborate than field stripping a standard AR for cleaning. When you’re done, you have a lightweight, maneuverable carbine for the 21st century that lets you lob a lot of lead downrange with speed and accuracy that might even give an Old West hero and his trusty “One of One Thousand” Winchester a run for his money.