Just Right Carbines Multi-Caliber Pistol Carbine Rifle 9mm Review

Just Right Carbines Multi-Caliber Pistol Carbine Rifle 9mm Review What is the Just Right Carbine? The JR Carbine is an ambidextrous, straight blowback-operated, semi-automatic, pistol-caliber carbine. All of that sounds interesting, […]

Just Right Carbines Multi-Caliber Pistol Carbine Rifle 9mm Review

What is the Just Right Carbine?

The JR Carbine is an ambidextrous, straight blowback-operated, semi-automatic, pistol-caliber carbine. All of that sounds interesting, but the most interesting part is that it can be reconfigured by the end user to shoot a variety of four different pistol caliber cartridges.

Just Right Carbines logoAbout Just Right Carbines, LLC

The company was conceived in 2009 in Upstate New York with the goal of engineering a simpler, accurate, more reliable and flexible carbine using common pistol calibers. Since those humble beginnings, Just Right Carbines now has more than 25,000 weapons in the field a short five years later.

Bob took the Just Right Carbine out in 9mm configuration and put together this video review.

As Bob said, he liked the Just Right Carbine a LOT. It ran well on multiple budget ammo brands and put up respectable groups at 25 and 10 yards. Bob noted that his wife, who is smaller in stature, especially liked the Just Right Carbine. However, because of the timing of when the rifle arrived Bob was only able to test the JRC in the original 9mm configuration. So, when Bob finished his review the JR Carbine and the .40 S&W caliber conversion kit were sent to Chris for further testing. More on Chris’s caliber conversion experience below.

How Just Right Carbines describes the product

Just Right Carbines ReviewProduct Features:

  • Semi-automatic pistol-caliber carbine
  • Simple, reliable, straight blowback operation
  • Ambidextrous bolt – configurable for left or right-hand ejection
  • Bolt/charging handle can also be moved to left or right side
  • Converts to other pistol-calibers with simple conversion kit (available separately)
  • Magazine included – Glock/Glock compatible or M&P depending on model
  • Lightweight 17″ barrel (U.S.) or 19″ (Canada)
  • Free-floating quadrail forend or takedown tube forend
  • Picatinny rail machined into top of receiver
  • Telescoping 6-position collapsible M-4 style buttstock or Fixed, depending on model
  • Receiver, trigger housing and magazine well machined from aerospace grade 6061T-6
    aluminum with black hardcoat anodizing for extra protection and durability
  • Standard M-4 buffer tube, buttstock, and pistol grip
  • Utilizes standard M-4/AR-15 furniture and trigger components
  • Lightweight – approximately 6.5 lbs.
  • Overall length: buttstock extended 33-1/2″, collapsed 30-1/4″
  • Made in the USA, in New York State

Glock Magazine Quadrail Model
Calibers: 9mm, .40S&W, .45ACP and .357SIG
Finishes: Black, Desert Camo, Muddy Girl, ReaperZ Green, A-TACS Foliage Green and Snow Ghost
Models: Standard, California, Restricted, SAFE Act

Chris’s review of the Just Right Carbine, including caliber change

Above you saw where Bob reviewed Just Right Carbine’s 9mm, Glock magazine, quad-rail carbine.  The product was a success. Nimble, accurate, and just plain fun to shoot.

This time I am reviewing Just Right Carbine’s .40 S&W (Glock magazine) conversion kit (with California legal bullet button!).

Brand Just Right Carbine
Model # Tested JRCCONV40
Finish/Stock Black anodized
Barrel Length 17”
Caliber .40 S&W
MSRP $299

*Cannot ship to: Canada

The kit includes

  • Illustrated Instruction Manual
  • Barrel
  • Complete Magazine Well
  • Complete Bolt
  • Ejector plate
  • Heavy Buffer
  • 10 or 15-Rd Magazine (depending on location and availability.  10-Rd magazine included with our test kit)
  • All Required Tools

The parts of this caliber conversion are many, but can mainly be broken down into 3 groups:

  1. Bolt/Upper receiver
  2. Magazine Well/Lower
  3. Barrel

40S&W Glock Caliber Conversion Kit‘Illustrated Instruction Manual’

The Illustrated Instruction Manual is an 8 page set of instructions that apparently was run off on someone’s laser printer. While it does contain several nice pictures of the carbine with parts labeled, it doesn’t include any exploded views of the parts to go along with each step.  As a result, performing the caliber conversion is NOT for the faint of heart!


‘All Required Tools’ are included with the conversion kit.  Despite this, right in the beginning of the directions under disassembly it tells you to clamp the gun in your gun vice or padded vice.  While I wouldn’t expect a vice to be included in the kit, a jig (probably 3d printed) for use with their carbine in your vice would have been nice!

Just Right Carbine upper receiverThe Upper Receiver

Keep close track of parts as they come out and go in.  Many of the parts appear to be caliber specific. You don’t want to mix and match parts from the different caliber kits by accident!  There are some good features here.  To start with, this is one of the few rifle kits out there which is EASY to switch from right handed to left handed!  Screw the ‘charging bolt’ on to the right side of the bolt and install the ejector plate so that the spent shells eject to the appropriate side!
I should point out here that as part of the conversion process you end up removing and then reinstalling the buttstock. As part of this process I ended up changing the buffer/spring.  While trivial, it is inconvenient that the buttstock doesn’t remain attached to the lower like it would in a full AR platform.

Just Right Carbine lower receiverThe Lower Receiver

I have to admit that I am not thrilled that the lower is connected to the upper with 3 hex screws instead of pins.  This is probably the first sign that this conversion is NOT something you want to do at the range or on the fly. Two of the screws connect the trigger group to the upper and the third ensures that the magazine well is properly aligned (after you slide the milled portion into place with the rest of the lower) to ensure good feeding of your rifle.
The original rifle we were sent had a standard magazine eject button installed.  The conversion kit came with a California legal bullet button.  The good news is that I was able to install the standard magazine eject in place of the bullet button though the fit was not great.  The bullet button would not install in the non-bullet button magazine well that the original carbine was provided with. One thing I have learned in doing reviews is that we often ask for odd configurations and end up with not all of the right parts. I think it throws some of the shipping departments off when we ask for combinations of parts that a normal customer might not ask for.

Just Right Carbine barrelThe Barrel

Installing the barrel is not hard.  Keeping all the parts tight after reassembly was another story!  After I performed the conversion, my barrel nut apparently loosened slightly resulting in cartridges tearing themselves in half after less than a magazine’s worth of shots! The directions don’t recommend putting on a few drops of Loctite blue on the barrel nut threading, but it probably would have stopped the barrel nut from working loose and the headspace changing.

Just Right Carbine quad rail handguardThe Handguard

Reinstalling the quad-rail handguard and getting it properly aligned and locked down proved challenging. Every time I managed to get it threaded down to the lock ring, they’d both shift and I’d be off to the races again getting them aligned. A nice long mount which could be run from the upper’s rail to the quad rail to keep them aligned would have been nice to have!

TJust Right Carbine review - 40 S&W brass separatedest Firing

As I mentioned in the barrel install section, the rifle developed a glitch after 8-9 rounds.  It would eject the bottom half of the shell and the top half would remain in the chamber. Among other things this prevented the next round from chambering completely. This made accuracy testing the rifle entertaining, yet time consuming, as I was able to remove the cartridge portion using a bore snake run in the wrong direction most of the time. We later determined that that barrel nut must have worked loose, creating too much headspace.
Other than the loading issues, I found accuracy at 50 feet to be more than adequate. Handling was nimble and shooting it on steel was all that I expected!



After the conversion was completed, accuracy and handling were consistent in 40 S&W as they were with the 9mm original configuration. I was unhappy with the complexity of the conversion and the fact that I apparently had headspace issues after a few shots (probably due to my technical proficiency installing the new barrel) might give pause to the average shooter.
Given the opportunity and flexibility of budget, I would recommend saving up the little bit extra and getting a second carbine in the desired caliber rather than buying the conversion kit in most circumstances. If, for example, business/professional requirements required changing your duty weapon from a 9mm Glock to a 40 S&W Glock, then I would recommend having a gunsmith or armorer help you install this conversion kit in your carbine to insure long term reliability and accuracy with this weapon system. At least the first time.

Gears Rating:

Gear Score
Just Right Carbines makes a fun little rifle that can be configured in any of four popular semi-auto pistol calibers. Conversions aren't for those short on mechanical aptitude, but are doable with patience and a little elbow grease. Accuracy appeared better than expected.


Defender Ammunition CompanyWithout the support of our ammo suppliers we would not be able to do nearly the amount of gun reviews that we do today.

Big thanks go to our Ammo Sponsor Defender Ammunition Company for supplying ammo for our tests and reviews on an ongoing basis. For this review we shot more than a few magazines of Defender’s 9mm and .40 S&W rounds.

About Jeff

Jeff is the Editor in Chief of Gear Report and a National Shooting Sports Foundation Media member. He reports on the outdoor industry, reviews gear for camping, hiking, shooting, hunting, paddling, backpacking and other active pursuits. A USAF veteran, Jeff earned a MBA in Marketing and Health Services. He specializes in consultative selling and internet marketing. As the VP of BD & Marketing, Jeff provides sales and marketing leadership to MGECOM, Inc. and helps http://MGECOM.com acquire new clients in need of solutions for online merchants in need of Affiliate Marketing program management. Jeff founded and manages Cress Sales & Marketing LLC, offering online sales and marketing consulting and services to online merchants and service providers.