Pistol-caliber rifles and carbines have been around for decades and have always enjoyed some popularity. There are a number of different reasons for this. Not only is pistol ammunition cheaper than rifle ammunition, it is much easier to hit something with a long gun than a pistol. Between that, the lack of recoil and quieter report, pistol-caliber carbines are a great choice for new shooters.
They also have a utility beyond that of simple target shooting, namely self-defense. Depending on the caliber and load, you'll see an extra 100 to 300 fps boost when firing pistol ammo out of a carbine-length barrel. Depending on the laws in your locale and the added boost in velocity you get, hunting might be an option as well.
I was introduced to the JR (Just Right) Carbine at a recent industry event and was surprised to learn it had already been around for a few years. Ironically, when I got a carbine in to test and showed up at the range with it, friends from Canada I shoot with knew all about the JR. They told me the JR Carbines are very popular up there, as they do not have the same restrictions on them as true AR-style rifles and carbines.
While it will take AR trigger groups, stocks, pistol grips and fore-ends, one look at the carbine will tell you it is not designed around the AR receiver. The JR Carbine is a straight-blowback carbine designed to feed from the Glock magazine.
Reliability is first and foremost, and the designers of the JR did a smart thing building it to feed from ultra-reliable Glock magazines. Even if you don't own a Glock, Glock magazines are everywhere, are reasonably priced and hold a lot of rounds. Even the Glock 33-round 9mm magazines aren't too expensive or hard to come by (if legal where you live, of course).
I obtained a 9mm carbine for testing for this article, but the JR is offered in .40 S&W and .45 ACP as well. If you want to change calibers, you don't have to buy a whole new gun. You can buy a conversion kit for $250 that includes a new barrel and, in the case of moving from the 9/40 to the .45, a new magazine well. That makes this a really versatile system.
This carbine is specifically designed to be simple, which is a good thing. Also, simple usually equals inexpensive, and such is the case with the JR. To keep their carbine inexpensive ($699 suggested retail for the basic model) the designers use a simple magazine release on the left side of the magazine well, similar to the layout you see on Glock pistols.
Both the charging handle and ejection are completely reversible. The handle just unscrews. Moving the ejection port cover from one side of the receiver to the other changes the ejection because the ejector is built into the inside surface of the cover.
The upper receiver is secured to the lower with two hex-head screws. The bolt handle reciprocates when firing, and it can be locked back with the use of a notch.
Both the upper receiver and fore-end are railed, so you can mount whatever optic you desire, but the carbine does not come with any sights. Versions are available with threaded barrels so you can install the AR muzzle device of your choice.
I have fired three JR Carbines extensively, two in 9mm and one in .40 S&W. All of them were completely reliable. In fact, I was shooting one 9mm carbine with my two boys and we put so many rounds through it in an afternoon (at least 500, most of which were steel-cased) it got so dirty I couldn't work the bolt by hand without smacking it loose, and yet it still kept running.
Prior to the next range session, where we put another 200 or so rounds through it, I didn't clean it but merely lubed the bolt through the ejection port, and we never had a problem.
However, all three JR Carbines suffered the same problem: The fore-ends got loose and unscrewed under recoil. This is a simple fix with Loctite, but it's something that should be addressed at the factory.
My two boys (ages 14 and 10) have fired several brands of AR-style pistol-caliber carbines, but they liked the JR Carbine better because the controls were simpler. They liked the bolt handle on the side of the receiver — they knew right where it was, and with the notch it was easy for them to figure out how to lock it back — something to consider if you're planning on buying a carbine kids will shoot.
Personally I prefer the look of a true "AR-15"-style pistol-caliber carbine over the JR Carbine, but those cost hundreds of dollars more than the JR and aren't any more reliable or accurate — or fun.