It has been said that with so many available accessories, the AR-15 family of weapons is like Barbie but for men. Calibers range from .22 to .50 and the number of stocks, pistol grips and other aftermarket accessories has never been matched by any other firearm, including the 1911 pistol.

MG Industries (MGI) has taken this adaptability to a whole new level with its MARCK 15 AR Hydra Modular Rifle System platform. The base system can be configured to many different rifles by changing the barrel, bolt, bolt carrier and magazine well to the desired caliber by using the base upper and lower receivers. The entire conversion process takes only a couple of minutes.

9mm Hydra “Barbie” as accessorized in text.
9mm Hydra “Barbie” as accessorized in text.

I recently obtained a 9mm Hydra carbine for evaluation. The carbine comes in a hard plastic case with upper and lower compartments separated by closed cell foam. The upper and lower receiver are in the top compartment, and the barrel assembly, magazine and instruction manual are in the lower. A quad rail is permanently affixed to the upper.

Hansen practices firing from cover with 9mm Hydra.

To attach the barrel to the upper receiver, unlock the retaining block’s safety bail (reminiscent of the old bails on Mason jars) and slide the retaining block forward. Next, rotate the two locking arms. This prepares the upper receiver to accept the barrel.

At the top rear of the barrel are a small locating pin and corresponding notch in the upper receiver. Insert the barrel until it is fully seated in this notch. Rotate the two locking arms back into position, slide the retaining block to the rear, and latch the safety bail.


To complete a conversion to another caliber, separate the upper from the lower and install the correct bolt carrier group. Depress the pin on the front of the trigger guard and rotate the trigger guard down. Depress the magazine release and lift off the magazine well. A different magazine well is installed in the reverse order.

It takes longer to read this than accomplish it; it’s that easy to convert from one caliber to another. Because only the barrel, magazine well and internal parts are changed, the Hydra system allows you to change calibers while retaining your favorite grip and stock on the base weapon.

The 9mm Hydra is blowback operated, so the gas key on top of the bolt carrier serves only to keep the BC properly aligned. I have to restake this part on some manufacturers’ rifles, but it was staked properly on the 9mm Hydra.

While most manufacturers mark the serial number and caliber on the magazine well, since this part on the MGI carbine is removable, the serial number is placed on the rear of the lower next to the safety. Caliber is designated as “multi.” The magazine well is marked with the caliber and magazine type. The 9mm ejector is fixed to the magazine well.

The 9mm Hydra comes with an M4-type six-position collapsible stock, A2-type pistol grip, and single 20-round 9mm Colt-style magazine made by C Products Defense. No sights are provided.

Since the Hydra assembles and disassembles so quickly, the compact hard case—approximately 17 inches wide by 14 inches high—can be used for discreet carry.

9mm Hydra as received.
9mm Hydra as received.


Let’s face it, for many folks part of the enjoyment of an AR is finding the right accessories and customizing it to meet your individual needs or desires—and I proceeded to do just that.


The first thing the 9mm Hydra needed was sights. I like red dot sights as they allow you to quickly acquire and engage a target if you are moving, the target is moving, or both. For this evaluation, I chose a Lucid M7 with the accessory riser that lets you see back-up sights (BUS) in the lower 1/3 of the glass.

In spite of its cast aluminum frame, the three-inch-long Lucid M7 weighs only 4.6 ounces. On/off/brightness buttons are easily accessible on the left side of the sight and are covered in a rubber material. It has seven brightness levels and can be set with an auto brightness sensor that will automatically increase the brightness of the two MOA dot in full sunlight and dim it in lower light conditions.

The M7 runs on a single AAA battery and features an auto shutoff after two hours to conserve battery life. The battery compartment and windage and elevation turrets are tethered together and sealed with a rubber “O” ring. Parallax free, the 1X sight has a field of view of 48 feet at 100 yards.

As reliable as red dot sights have become, I believe having back-up sights is a good idea. As the saying goes, “stuff” happens…. I went with Magpul’s MBUS sights front and rear. Designed to fit an M1913 Picatinny, the front MBUS is adjustable for elevation (sight tool included) and the rear is adjustable for windage. In the folded position, each takes up only 2.6 inches of rail space. MBUS sights are spring loaded; pressing a latch on either side of the sight’s base allows them to be deployed quickly with either hand.

Bail open, safety block moved forward, and locking arms open to receive barrel.
Bail open, safety block moved forward, and locking arms open to receive barrel.


I replaced the M4-type stock with an Ergo Grips Pro Stock. This stock comes with its own overmolded receiver extension (buffer tube) and end plate. Instead of the usual six, the Ergo Grips Pro Stock has eight positions of adjustment. The end plate has sling points and there are socket-type sling points on the stock in addition to slots that a sling can be attached to. This stock makes the gun a bit heavy toward the butt end, but at the same time makes it easier to drive.

On a side note, the castle nut on the supplied stock was properly staked, showing MGI’s attention to detail.

Bail and safety block in closed, locked position.
Bail and safety block in closed, locked position.


I’m sure the A2 pistol grip fits the hand of the person who designed it, but it has always felt uncomfortable to me. My general practice is to remove some or all of the finger bump with a sander or use an aftermarket grip that fits me better.

I replaced the A2 grip with an Ergo Grips GripSure, which is made with a rubber-like material and has Ergo Grips’ Rhino Hide™ texturing. While the grip has finger grooves, they flow gradually from one to the next and do not force your fingers into one position. The top of the grip is wider than the bottom, conforming more naturally to the hand. The GripSure also comes with The Gapper—a piece of rubber that fills in the annoying gap between the trigger guard and pistol grip.

Quad rail is permanently attached to upper receiver.
Quad rail is permanently attached to upper receiver.

White Light

Any long gun that may possibly be used for self-defense should be equipped with a white light. Some people disagree with this, but the fact is that you cannot legally or morally shoot at someone without positively identifying them as a threat.

I mounted a Streamlight TLR-4G at the end of the rail in the nine o’clock position. The LED light emits 115 lumens in conjunction with a 510-530nm green laser. The TLR-4G has a three-position toggle switch at the rear of the unit for laser with white light, white light only, and laser only. A rocker switch allows both momentary and constant on, regardless of which position the toggle switch is in.

The TLR-4G uses a single 3V CR2 lithium battery (included) and has the following run times:

• LED only: 1.75 hours
• LED and laser: 1.25 hours
• Laser only: 4 hours

Since the laser, as mounted, sits three inches from the center of the muzzle, mechanical offset must be taken into account just as when sights are used.

Where nothing was mounted, I protected the “cheese graters”—and my hands—on the quad rail with Ergo Grips Textured Slim Line rail covers.

Unique magazine well is removed by rotating down trigger guard, depressing magazine release and separating it from lower receiver.
Unique magazine well is removed by rotating down trigger guard, depressing magazine release and separating it from lower receiver.


I enlisted the assistance of my son Flint and grandson Austin to evaluate the 9mm Hydra. As mentioned, the 9mm Hydra ships with a single 20-round magazine. In order to spend more time shooting and less time jamming a single mag, I requested and received two additional magazines from MGI. I also received six 32-round magazines from C Products Defense.

We arrived at the range with a wide assortment of 9mm loads: 14 loads from seven manufacturers and a handload. Bullets ranged in weight from 50 to 147 grains, and bullet profiles included full metal jacket (FMJ), jacketed flat point (JFP), jacketed hollow point (JHP), and lead round nose (LRN).

Zeroing the Lucid M7 was a snap, with the first five rounds perfect for elevation and only about two inches to the left. Taking into account common engagement ranges for private citizens and peace officers, we shot ten-round strings through the carbine at 25 yards from kneeling for groups.

Gas key was properly staked—a step some manufacturers skip.
Gas key was properly staked—a step some manufacturers skip.

All went well until I came to the last round to be tested: the Double Tap 124-grain +P. The first round—number 141—had a catastrophic case failure just ahead of the case web, splitting halfway around the case, blowing the magazine out the bottom of the mag well, and peppering my face with small fragments. After giving the carbine a thorough check, I did something I highly advise against: I fired a second round of the same ammo … with the same results. Testing of this round ceased at that point. I took a closer look at other cases and many had a visible bright spot at the same point, running about one-third around the case.


Using a 30-round magazine as a monopod from prone has become common practice. The myth that this causes malfunctions has been thoroughly debunked. Not so with the Hydra, at least in 9mm. After accuracy tests were performed the same way for each load, I fired several strings using the 32-round mags as a monopod and experienced several Type II (stovepipe) malfunctions. Using the same mags and ammo but firing without resting the mag on the deck resulted in no malfunctions. My best guess is that, although the mags locked up solid, there must have been enough pressure to cause the top round to put increased pressure on the carrier, slowing it down just enough to create a malfunction.

Carbine comes with an M4-type stock, but was replaced with Ergo Grips Pro Stock.
Carbine comes with an M4-type stock, but was replaced with Ergo Grips Pro Stock.

We also fired several strings from 50 yards standing, and the carbine kept the rounds within eight inches. Velocity for each load was established by firing ten-round strings using a PACT Professional Model chronograph, with the first screen ten feet from the muzzle. A comparison of the velocity fired from the 9mm Hydra’s 16-inch barrel and the DB FS Nine’s 4.75-inch barrel (POLYMER PROTECTOR: Diamondback Firearms DB FS Nine Pistol, August 2014 S.W.A.T.) appears in the accompanying chart.

Most of our shooting was performed at 25 yards and closer. We included firing while moving off the line of attack, shooting on the move while advancing on a target, multiple targets, barricade shooting, and shooting while moving backwards to cover.

The 20-round C Products Defense magazines worked perfectly, as did the 32-round mags, although the 32-rounders did not always actuate the slide lock—not a deal breaker for me after firing 32 rounds.

Catastrophic case failures with 124-grain +P.
Catastrophic case failures with 124-grain +P.




When I returned home, I removed the barrel and there was a very slight build up only about .040 from the end of the chamber. This build up was enough to set the cartridge back under the feed ramp, where it has less support, and create the bright spot on some cases and the failure of the +P Double Tap load. Scrubbing the chamber with a bristle brush wet with Weapon Shield solvent removed the buildup.

If I have complaints about the carbine, they concern what items are not included. The Hydra is furnished with one magazine. Manufacturers need to realize that extra magazines are not “accessories”—they are an integral part of the weapon. It also would not raise the price much if MGI were to include a set of iron sights like the Magpul MBUS used in this evaluation. Sights, like magazines, are needed to make rifles fully functional.

MG Industries Hydra Modular Rifle System is one of the most unique systems I’ve seen in many years. The ability to quickly change calibers and different magazines—for example 7.62x39mm with AK mags to 5.56mm and standard AR mags to 9mm with Colt-type SMG mags in just minutes—puts the MGI Hydra system in a class of its own.


MG Industries
(207) 817-3280

ASYM Precision Ammunition
(970) 385-7900

Black Hills Ammunition
(605) 348-5150

C Products Defense
(941) 727-0009

Ergo Grips
(877) 281-3783

Double Tap Ammunition
(866) 357-10MM

Federal Cartridge Company
(800) 322-2342

Hornady Mfg. Co.
(800) 338-3220

Liberty Ammunition
(941) 567-6178

(307) 840-2160

Magpul Industries Corp.
(877) 462-4785

(800) 722-8462

Streamlight, Inc.
(800) 523-7488

Winchester Ammunition
(615) 258-3340

Leave a Reply

Your email address will not be published. Required fields are marked *

You May Also Like