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GM6 Lynx: 12.7mm Industrial Hole Punch

Photos by Kenda Lenseigne

There’s something very Victorian and steampunk-esque about the GM6 Lynx. It has the proportions of a steam locomotive or a traction engine, and its mechanism ker-chunks back and forth like an ancient machine tool. 

But there’s also an element of Starship Troopers in its monstrous bullpup design. While none of us would want to spend an entire afternoon plinking tin cans with it, it got us rethinking our abusive relationship with big-bore rifles. For a .50 BMG, this one’s actually pretty fun to shoot.

The GM6 is a bit of an anomaly in that unlike most semi-auto centerfire rifles, it eschews any form of gas operation. Instead, it borrows its layout from a shotgun, the venerable Browning A5, first produced in 1902 and designed by the prophet (pbuh) John Moses Browning. 

See that brake at the business end? If you shoot this thing, you’ll come to appreciate it as much as we did.

JMB went on to use the same long recoil mechanism in the Remington Model 8 rifle introduced in 1905, which in turn inspired the Worst Machinegun of WWITM, the Chauchat. After that, the development of long recoil firearms in general fell into a black hole, and apart from the weird Frommer Stop handgun of 1912, and a product improved version of the A5 made by Remington, nothing else of note was ever produced that employed this operating system. Until now.

Given the dearth of guns using it, it’s probably worth a recap of long recoil operation and its strengths and weaknesses. When a round is fired, the barrel and bolt are locked together to contain the pressure generated by burning powder. 

Newton’s third law kicks in, and both bolt and barrel start recoiling together inside the receiver in reaction to the bullet proceeding up the barrel, but as they’re much heavier than the bullet, it has time to leave the barrel before things really get rolling. When the bolt and barrel reach the end of their recoil stroke, the bolt unlocks and is temporarily held to the rear against the force of its recoil spring, while a separate spring pushes the barrel back into battery, ejecting the fired case as it goes. 

As you’d expect, everything about the GM6 is big, scaled around the .50BMG cartridge. We chose accessories accordingly, and the Trijicon Tenmile scope and Spartan Precision Kratos bipod both stood up to almost 100 rounds of ball and APIT. Which was quite enough, thanks.

Once the barrel is back in position, it trips a lever to release the bolt, which moves forward, picking up a fresh round from the magazine. Without a gas system, the mechanism has fewer moving parts, and hence fewer things to go wrong. 

But getting the gun to work with different types of ammo is usually more involved than simply twisting a gas regulator, and due to the barrel not being fixed in the receiver, accuracy tends to suffer. When adopted by legendary lawman Frank Hamer, the Remington Model 8 was typically a minute-of-bank-robber rifle. Ask Bonnie and Clyde.


The GM6 is designed and produced in Hungary by Sero International and imported to the USA by Anwika LLC. It’s expensive (but then, everything associated with .50 BMG rifles is) and rare; we got our hands on one of just 40 that are in the country at the moment. 

When you first heft it and manipulate the controls, it feels like it’s hand built in an Eastern European workshop populated by old guys in oily dungarees, each one of whom has worn a low spot in the wood flooring next to his workbench and expertly wields a file with a cigarette hanging from his lip. Not having visited the factory (yet), we can’t say if this picture has any ring of truth to it — in reality, it’s probably a product of brightly lit and clinically clean CNC machining centers, but we’ll hold onto the mental image for now. 

Let’s look at this beast from stem to stern. Up front is a large, single chamber muzzle brake that, trust us, you come to appreciate very quickly. It’s attached via left-handed threads to a 29-inch-long barrel, which for a 50, has a fairly slender profile at the loud end.  

During firing, the entire barrel and bolt group recoil to the rear, softening the recoil impulse considerably, but at the cost of increased dust signature. Here, the action hasn’t quite reached the rearmost position of its stroke, and the bolt and barrel are still locked.

Attached to the barrel about a foot behind this is a bushing that reciprocates with the barrel and keeps the front end tight in the receiver, the front of which has a manually operated catch to lock the barrel in its rearward position, shortening the gun’s overall length by six inches. In this state, the GM6 is about the same length as a 16-inch barreled AR-15. 

Previous versions of the GM6 arrived in the USA with a bipod attached to the catch assembly, but the ATF decided that this was beyond the pale. Who knew bipods were so deadly? Anyway, the agency best known for immolating children and pulling decisions out of its collective arse has since reversed its position (surprise!), so future iterations of the gun will once again be able to stand up on their own. 

In the meantime, our friends at Spartan Precision sent over a prototype of their new Kratos bipod, designed specifically for beasts like this one. Made from 7075 T6 aluminum and carbon fiber, it’s built to handle 50-cal recoil and, like Tiny Tim, ask for another helping. 

The catch that holds the action to the rear can be seen just forward of the bipod. This allows the shooter to maintain a shorter overall length and empty chamber. When disengaged it’ll send the working parts forward, chambering a round in the process.

An 18.5-inch-long, 20 MOA Pic rail is attached to the upper receiver, and to this we added a Trijicon Tenmile 4.5-30×56 scope. Its 34mm main tube gives a whopping 100 MOA of adjustment, which coupled with the angled rail gives plenty of adjustment out to the horizon. If that isn’t enough, you can always hold an extra few MOA in the reticle. 

The GM6’s controls are fairly conventional, with a crossbolt safety and exposed magazine release catch at the rear of the pistol grip. Its trigger is very bullpuppy (is that a word? If not, it should be) but isn’t the worst we’ve encountered. 

There’s about a ¼ inch and 2 pounds of take-up in its first stage before hitting a wall, then a long, mushy rollover break, topping out at about 5 pounds. We were initially concerned that this would make precision shooting more difficult, but we needn’t have worried — more on this later. 

The crossbolt safety can be seen just behind the trigger, while the charging handle can be seen in its folded position above the magazine.

The rifle lacks a last round bolt hold open, but with a claimed five rounds on board, it’s unlikely you’ll lose count of how many you fired, and its single stack magazine slides in a dovetail at the rear of the pistol grip and locks very securely in place, despite the absence of any kind of magwell. While the manual lists its capacity as five rounds, it’s possible to load a sixth without malfunction. 

Getting the gun into action is slightly unusual due to its operating system. While you can haul back on the charging handle to hand cycle the first round into the chamber, you’ll be dragging back not only the bolt but also the barrel, not to mention compressing two recoil springs as well. 

The smart way to do it is to lift up on the charging handle first, unlocking the four-lugged bolt from the barrel extension and allowing the bolt alone to be pulled rearward before letting fly to strip the top round from the mag. 


There’s always that moment of anticipation when touching off a new 50 for the first time. After all, this is a cartridge that’s dangerous at both ends — a case head separation in a 9mm or 5.56 won’t make for a great range day, but the same event in a BMG could result in a trip to the hospital. 

Burning more than 10 times the powder charge of a .223 with every trigger press is nothing to be sniffed at, so first shots after cleaning the preservative grease from the chamber and bore tend to raise the blood pressure a tad.

Bullpup layout means that the GM6 is shorter than you expect, given the caliber.

We needn’t have worried. Sure, there’s a lot of commotion going on between the enormous muzzle blast, reciprocating iron, and 624-grain projectile, but the GM6 has a very smooth recoil impulse, spread out over what seems like an eternity. Granted, its nearly 30-pound all-up weight dampens things a bit, but it mostly comes down to the effective brake and novel operating system. Our first two shots resulted in a failure to feed, requiring us to haul back on the bolt handle, but after that it was plain sailing, with all brass landing in a neat pile about a foot from the gun. 

We used CBC M33 ball ammo, along with a handful of homebrewed APIT loads, which were used to check function and bust rocks rather than punch holes in our steel targets. 

Barrel bushing to the right is replaceable and ensures a tight lockup when the action is in battery.

50 BMG is more difficult than most cartridges to wring out match-grade accuracy, and in our experience shooting ball ammo from a semi auto, you can count yourself lucky if you’re able to achieve 3 MOA groups. And so it was with the Lynx. 

If we invested time to develop a load for it using premium components and take care with case prep, we might see things tighten up, but unfortunately the constraints placed by deadlines meant this wasn’t going to happen. 

For its intended role as an anti-materiel rifle, or plinking at moving MTLBs, we could see it working just fine. For a sniper pair working out of vehicles or in an urban setting, its compact dimensions are a huge plus, especially when collapsed to its shortest length, and due to its long recoil system, it offers comparatively rapid follow-up shots. 

As a bonus, when moving in an infantry squad, the 50-cal gunner won’t stick out like the balls on a greyhound and attract unwanted attention from UAVs. 

Unlike most rifles of this caliber, the GM6 Lynx is pleasant to shoot — actually, scratch that — it’s not flinch-inducingly obnoxious, which means that the risk of ruining your personal accuracy potential is considerably less. 

As a yardstick, we offer this — we’d rather shoot the GM6 than a 12-gauge with low recoil slugs, as a big push is better than a quick slap. The U.S. importer is currently working on a domestically manufactured suppressor, so you’ll hopefully see it on the line at the next RECOIL CANCON event in Arizona in April 2024. 

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