Pistol Caliber Carbine Perfection

JP Rifles’ GMR-13.

Pistol caliber carbines are not something new. Cowboys routinely relied on a lever-action rifle that used the same ammo as their revolver. After all, when wandering the range you could only carry so much kit on one horse and the ability to share ammo between your rifle and revolver seemed to be a savvy solution. Nowadays there are not too many folks relying on horses or who are armed with a .32-20, .38-40 or .44-40 Colt Single Action but there are tons of folks carrying a 9mm.

The AR-15 has supplanted the lever-action rifle as America’s Rifle. And, with all the more modern cartridges, specifically the .223 Remington, does it make sense to be armed with a pistol caliber carbine? Is it practical for your long gun and handgun to have ammo compatibility? The answer to both these questions is like it is with many theoretical firearms questions—it depends.

If you want to whack bad guys at 300 yards or go hunting for small or even large game with your long gun, its hard to argue a pistol caliber carbine is the best choice. Yes, the cowboys did it but in reality, they didn’t have a lot of options. Modern gun guys can have a 9mm sidearm and an AR in .223 Remington, or even some infinitely sexier cartridge, and do about anything they want. So what is the appeal?

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If there is a fault with the standard AR-15, it is that you can’t easily run
the action manually while the carbine/rifle is on your shoulder. With the side
charging handle on the JP Rifles’ GMR-13 this is not an issue.

A Niche Weapon

Let’s not look at the big picture and try to justify an AR chambered for a pistol caliber by arguing it will do anything we want done. You are limited in what you can do with a pistol caliber carbine. It is, by nature of the cartridge, a relatively short-range weapon. Sure, you can get hits at 300 yards with a 9mm carbine but terminal performance will be drastically reduced due to velocity loss. And, your trajectory will look like a 50-yard pass on the gridiron.

Lack of recoil is the primary advantage an AR in 9mm offers. An AR in 9mm becomes almost as controllable as one in .22 LR. Another thing you will find, if you are shooting indoors, is that the muzzle concussion/blast is drastically reduced from what you will experience with an AR in .223 Remington. This is the result of firing a cartridge operating at about half the pressure of the .223.

Then there is the subsonic option. When working with an AR designed to fire high-pressure rifle cartridges, the use of subsonic ammunition becomes problematic. About the only way to guarantee reliable operation is with an adjustable gas block. This is because subsonic ammo runs at about half the pressure of supersonic ammo. Additionally, the heavy for caliber bullets used in subsonic rifle ammo will rarely expand so terminal performance is reduced to punching caliber-sized holes.

With pistol cartridges in the AR none of this is a problem. Subsonic ammo runs at the same pressure of supersonic ammo so the reliable cycling of the AR’s action is not an issue. Given the velocities pistol bullets are designed to operate at, good subsonic terminal performance is achievable. Finally, a pistol caliber AR, firing subsonic ammo, is very, very quiet.

Additionally, you do have the benefit of only worrying about warehousing one type of ammo. If you are preparing for the end of days, a natural disaster or the zombie hoard, you can buy ammo of one type—in bulk—and live with the satisfaction no matter which box of ammo you pick up, it will work in both your handgun and your rifle/carbine.

The argument could go on and on, and ultimately I believe if you want a rifle, get one that fires a real rifle cartridge. But at the same time I have to admit, there are some good things about a pistol caliber AR. I wanted to give one a solid workout to see just what could be done with it so I contacted JP Rifles and asked for one of their excellent GMR-13 carbines in 9mm to test.

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The JP Rifles’ GMR-13 has a mag well with a wide mouth,
which allows for easy insertion of the Glock magazine.

The JP Rifles’ Answer

Like all JP rifles, the workmanship on the GMR-13 was superb and the carbine has a number of features worth noting. The triggerguard on the lower receiver is integral, meaning, there is no gap at the front of the Hogue grip to chew on the middle finger of your shooting hand. It comes standard with a tubular aluminum, rifle-length JP handguard fitted with an 11.5″ Picatinny top rail. A forward assist, Tactical Intent T-17 collapsible stock, ambidextrous safety lever and JP Compensator are also standard features. And, since this carbine operates on the blow-back concept, there’s no gas system.

The coolest feature was the dual charging system. In addition to the standard AR-15 charging handle, which is positioned at the top rear of the upper receiver, the GMR-13 has an additional charging/operating handle on the left side of the upper receiver. This is a great addition to the AR-15 because it allows the user to manipulate the action without ever removing his shooting hand from the grip. The non-reciprocating folding lever, which operates along a dovetailed rail on the left of the receiver, is large, easy to grasp and with a little practice, speeds up the manual operation of the action.

Granted, you’ll need to learn a new manual of arms for the AR platform, but after running about 200 rounds through this carbine I adapted to it quickly. However, one aspect of manual operation did not change. It is almost impossible to operate the action using the left side-charging handle while locking the bolt to the rear. Locking the action open is best done by pulling the standard charging handle with your shooting hand and depressing the bolt lock with your support hand thumb.

One last comment about the mechanics of the GMR-13 deals with the magazine release. It is an oversized pad about .75″ square. Yes, it is located in the same place as a standard AR-15 magazine release but it is much larger and much easier to depress. Oh, and yeah, the GMR-13 runs on standard Glock model 17 or 19 magazines. This means if your sidearm is a Glock 17 or 19, your GMR-13 will use the same ammo and the same magazines. This is a good thing no matter how you look at it.

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Like every rifle from JP Rifles, the workmanship on the GMR-13 was surperb.
Richard liked the dual charging system best.

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So what’s the deal with a pistol caliber carbine like the JP Rifles’ GMR-13?
Inside 100 yards it’s one of the fastest ways to put lethal hits on a target.

On The Range

For accuracy testing I mounted a Trijicon ACOG on the GMR-13. Zeroing was accomplished with just a few shots and then I began firing 10-shot groups at 50 yards. The first 10-shot group was fired with Hornady’s 124-grain Steel Cased Match HP ammo. That group measured just less than 1.5″, which is pretty amazing. Remington’s 115-grain MC load turned in a 2.5″ group and Federal’s 124-grain HST +P load, thanks to a single flyer, put 10 shots into a 3″ cluster. This is plenty good enough accuracy for headshots at that distance.

For the most part, at 100 yards, groups doubled in size and the point of impact was about 3″ below the point of aim. From the prone position at 300 yards I could hit a man-sized steel torso silhouette target about half the time but had to apply 8’—33 MOA—of correction. The 9mm carbine might not be pinpoint accurate at that distance but you could for sure make a bad guy get behind something. And stay there for as long as you had loaded magazines to feed the GMR-13.

It’s unlikely anyone will be singing the long-range virtues of a pistol caliber carbine and I won’t either. That is not the forte of the weapon system. A pistol caliber carbine, like the JP Rifles’ GMR-13, is best suited to fighting it out with bad guys where the distance to the threat is within tobacco spitting or breath smelling range.

To see how the GMR-13 performed when things got up close and personal I arranged some Action Target PT Hostage steel targets in a fan at 3, 5 and 7 yards. With a full Glock 17 magazine I began running single and multiple target drills. I was pleased with the results. Out to seven yards I could put five to seven shots in the center of the silhouette in about 2.5 seconds. It wasn’t a matter of keeping the carbine on target; it was simply a matter of how fast I could pull the trigger.

I also pushed the carbine through a common pistol drill known as the El –Prez. In this drill you turn and fire 2 shots at 3 different silhouettes, reload and repeat. If you can do this within 10 seconds with a handgun and get all your hits inside a 10-inch kill zone, that’s considered pretty good. I completed this drill multiple times with the GMR-13 in around 8 seconds without any misses.

Yes, a carbine is harder to manipulate in close quarters and almost impossible to conceal. But, if you need to put hits on target it is much easier to do so with a pistol caliber carbine like the GMR-13 than it is with any handgun chambered for a reasonable defensive pistol cartridge. This is even truer if the distance to the threat reaches out beyond 25 yards or even closer to 100.

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Hornady’s Steel Match 124-grain HP ammo shot incredibly well out of the
JP GMR-13 carbine. This 50-yard, 10-shot group was less than 1.4″.

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Though not as accurate as the Hornady load, Remington’s 115-grain MC load
shot well out of the JP GMR-13. Better than you can expect to shoot a
handgun at 50 yards.

Terminally Speaking

Terminal performance is important and with a 16″ barreled pistol caliber carbine you can expect a velocity increase of between 100 and 200 fps. Pushing bullets 20 percent faster than they were intended to go can have an impact—pardon the pun—on how these bullets perform after they hit something.

Testing in 10 percent ordnance gelatin has shown this additional velocity will increase the penetration of expanding bullets by an average of about 4″. And, while recovered bullet diameters are often smaller, damage to the inside of the gel block increases dramatically. What you do not get with a pistol caliber carbine is a bullet that is less likely to over penetrate. What you do get is a bullet that will damage greater amounts of tissue.

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One flyer opened the 10-shot group fired with Federal’s HST 124-grain +P
load to 3″. The remaining nine shots grouped into 1.5″.

In The End

If I could only have one carbine it would without question be one chambered for the .223 Remington. It has more reach and a wider application than any pistol caliber carbine. But, when and if the end of days arrives, ammo availability will become an issue and there is undoubtedly an advantage to being able to carry one type of ammunition for both your handgun and pistol, especially if they both use the same magazine. However, you might not be able to find 9mm ammo so having an alternate weapon—a .223 carbine—might not be a bad idea either.

Regardless which direction you might go, I can tell you this; the JP Rifles’ GMR-13 in 9mm is impeccably reliable, accurate and easy to shoot fast. It is one of, if not the finest, pistol caliber carbines I have ever fired. When the balloon goes up it would be nice to have a carbine you could say those things about! 
By Richard Mann

For More Info: JP Rifles
www.jprifles.com
(651) 426-9196

Specifications: JP Rifles’ GMR-13

Caliber: 9mm Luger
Barrel: 16″, JP Supermatch, button-rifled, air-gauged, cryogenically treated.
Overall length: 34.75″
Weight: 7 lbs., 4 oz.
Stock: Tactical intent T-17, collapsible
Sights: None
Action: Blow-back
Finish: Hardcoat, anodized
Capacity: 17+1 (uses Glock model 17/19 magazines
Price: Upper assemblies starting at $800. Complete rifle, price on request.

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