We’ve often referred to the AR platform as LEGOs for adults, because you can build and configure them to your heart’s content. However, there’s a limit to that analogy. You don’t need tools to tear down and rebuild your LEGOs. 

As flexible as it is, a standard AR lower can’t accommodate longer cartridges like 7.62 or 6.5CM; you’ll need to switch to a large frame AR for that. And it takes tools and some effort to swap out barrels. To be fair, Eugene Stoner invented the thing in the 1950s.

Idaho-based Primary Weapons Systems is well-known for its piston-driven ARs, components, and muzzle devices. The word “evolve” was a key element of their branding, with a line of products over the years that refined and improved existing platforms. 

But this time, PWS didn’t want to make an evolutionary product; they wanted to shake things up with their vision of a next-generation rifle. They wanted it to be a universal platform, adaptable by the end user to serve a multitude of different applications. 

So, PWS went back to the drawing board to create a truly modular rifle, taking the LEGOs concept to the extreme with its new UXR weapon system. 

USER XCHANGEABLE RIFLE

Surveying developments in the market, PWS benchmarked weapons such as the FN SCAR, SIG Sauer MCX, Remington ACR, and HK 433 that all offered various enhancements over M4s and AR-15s, though at significant price premiums. The company also took note of the conflict in Ukraine, where warfighters in the same unit were carrying a wide variety of different rifles in different calibers, not to mention possessed of varying levels of training with their weapons.

PWS distilled a list of features and capabilities that it wanted to incorporate into its next-generation rifle: user-configurable barrel, folding stock, ambidextrous controls, modularity for multiple configurations, and a simple, consistent manual of arms throughout. It should be able to serve as a duty weapon, precision rifle, competition rifle, or compact CQB gun, in calibers from 5.56mm to 7.62x39mm to 6.5CM. It should combine all the great feature sets that people have loved about the rifles that preceded it.

PWS is pretty synonymous at this point with piston-driven guns, and the UXR is no different. PWS calls it a “modified long-stroke” piston system. However, the traditional definition of a long-stroke system is that the gas piston is attached to the bolt assembly, like an AK-47 or PWS’s own piston ARs. The UXR’s piston isn’t fixed to the bolt carrier group, so technically it’s a short-stroke system such as the AR-18. However, PWS designed it to travel a full inch, much more than typical short-stroke systems. So, it’s probably more accurate to call it a long-travel short-stroke system.

Semantics aside, the end result is an operating system with the reliability, cooler temperatures, and cleanliness of piston guns, the lighter reciprocating mass of a short-stroke system, and the gentler shove of a long-stroke system’s recoil impulse.

The company came up with an ingenious modular design comprised of several separate, key components — an upper receiver with a trunnion, barrel assembly, trigger housing, magwell, trunnion cover, handguard, and buttstock.

The upper receiver is the serialized component of the firearm. It’s monolithic, with 18 inches of uninterrupted top rail for all the optics, lasers, and attachments you might desire. It’s 7075 aluminum, with 17-4 stainless steel guide rails for the bolt carrier group to provide maximum durability. It also houses the forward, non-reciprocating, reversible charging handle, which also doubles as a forward assist if, for instance, you need to very quietly chamber a round (it decouples from the bolt once it’s in battery).

The trunnion is made of titanium for longevity and clamps on the barrel assembly with three cross bolts across approximately 4.75 inches, providing return-to-zero within 0.5 MOA when torqued to the same spec. To change barrels, loosen the cross bolts, retract the bolt, and slide the barrel out. A locator pin and notch align the barrel for installation.

Our sample gun came chambered in .223 Wylde, with a 16-inch, 1/8-twist 4150 nitrided chromoly barrel manufactured in-house. PWS guarantees 1 MOA accuracy with good ammunition. The barrel has a taper lock shoulder to ensure alignment and ships with PWS’s new FRC compensator, tapered and threaded for the Plan B suppressor mounting system. It’s very effective by itself and convenient to attach a can.

Interestingly, the barrel also sports a bulge in front of the gas block reminiscent of tanks like the M1 Abrams. Indeed, it’s a bore evacuator, just like on those armored vehicles. Made of titanium, it siphons gas into a reservoir as the bullet passes; once the projectile exits, the pressure differential draws gas out of the barrel — less gas to come back in your grill.

Additionally, an extractor support pin provides strength for potentially dangerous overpressure events, such as squibs.

There’s also cutouts to access a three-position gas valve for normal use, suppressed, and adverse conditions. Ours required quite a bit of force to turn, but the difference between settings was noticeable.

The polymer trigger housing is also very clever. It takes standard AR grips and most drop-in triggers. A metal housing within the polymer housing secures them with two pins as usual, and you can release it with the press of a button. PWS includes an excellent TriggerTech single-stage trigger, adjustable from 2.5 to 5 pounds.

The ambidextrous safety selector is perfectly positioned, with positive and clean actuation, and 50 degrees of rotation between safe and fire. 

The magwell slots in front of the trigger housing. It’s made of polymer and comes in different variations to accommodate various calibers and magazine types. The receiver is sized for 7.62, so the 5.56 magwell has some extra dead space in front of the trigger guard. The ambidextrous magazine release and bolt catch are contained in the magwell component. Due to the design of the magazine latch, the button on the right side is a little stiffer than the one on the left; for once, it pays to be wrong-handed.

Right in front of the magwell is a polymer trunnion cover, stippled for grip and rounded for comfort. We’d have preferred it to be flat for bracing; it’d look better too, but beauty’s in the eye of the beholder. Notably, it’s also modular and removable — PWS plans to use this interface to attach heavy accessories; think underslung munitions.

The handguard has M-LOK slots at 1, 3, 6, 9, and 11 o’clock. It slides on from the front and is secured with a captured take-down pin. The shortest handguard accommodates a 10-inch barrel.

The rear of the trigger housing has a Picatinny rail, to which PWS’s folding buttstock is attached. You can reverse it to fold on either side, and it’s slightly tilted to clear the ejection port. The stock is aluminum for strength and stiffness, with an adjustable cheek rest and 2.5 inches of telescoping length of pull adjustment.

There are QD sling sockets built-in to the rear of the receiver and buttstock on both sides. Up front, you’ll need to use one of the M-LOK slots to attach your sling.

MODULARITY MASTERCLASS

Disassembling the UXR reveals its inventive design. First, remove the magazine and ensure the weapon is unloaded. Push out the rear captured takedown pin, then pull the trigger housing group directly to the rear to remove it. If you wish to service the trigger, push the button inside the housing to release the safety selectors on either side. Then, you can pull the trigger pack out.

Returning to the upper receiver, push in and downward on the guide rod mount at the rear to release the recoil spring assembly. It’ll slide out, along with the bolt carrier group. To disassemble the BCG, pull out the captured firing pin retaining pin and release the firing pin and spring. Then, remove the cam pin and pull the bolt head out of the front of the carrier. 

Like the trigger group, the magwell slides on a tongue and groove to the rear and can be pulled down and off once you align it with relief cuts in the receiver.

To remove the barrel, loosen the trunnion screws 1.5 to 2 turns. The barrel assembly can then come out the front, followed by the piston rod. You can remove the gas valve from the barrel for further cleaning. Removing the trunnion screws entirely allows you to detach the trunnion cover, for example to convert to 7.62x39mm rock-n-lock mags.

And all you need to swap the charging handle to the other side is a spent casing. 

To change calibers, swap barrels as well as bolt heads and magwells, if applicable. Certain configurations may require a shorter gas system and piston.

GOING HOT

There are so many cool aspects of the UXR’s design to talk about that we’re almost out of room to discuss how it shoots. In short, it shoots great.

Kitting it out, we attached a Vortex Razor HD Gen III 1-10x scope in a Scalarworks LEAP mount. The Vortex offers fantastic glass, bright illumination, and a first focal plane Christmas tree reticle. And the LEAP mount delivers the glorious OCD we’ve come to expect from Scalarworks. Up front, we mounted SureFire’s brilliant Scout Light Pro Dual Fuel, which spits out 1,500 lumens of light while attaching via a compact, built-in M-LOK mount.

We took advantage of the UXR’s FRC compensator by installing a Plan B HUB adapter from Wolfpack Armory on our PWS BDE suppressor. The Plan B system is light and compact, with a taper in front of threads to secure your silencer consistently and cleanly. It worked swimmingly with our rifle and can. 

We shot the UXR unsuppressed from bags on the bench to check accuracy and muzzle velocities, shooting five-shot groups and metering with our trusty Garmin Xero C1 Pro. 55-grain pills were the rifle’s least favorite, with Igman from Global Ordnance and American Eagle both posting bests of 2.7 MOA at 3,019 and 2,965 fps, respectively. Federal’s Fusion 62-grain bonded softpoint hunting ammo delivered 1.8 MOA at 2,776 fps. The UXR loved 69-grain Sierra Match Kings, with Gorilla achieving 0.87 MOA at 2,750 fps and Global Ordnance’s ADI topping the chart at 0.79 MOA at 2,667 fps. Needless to say, we were pleased with the results.

Ergonomics are great, with the TriggerTech excellent as usual and the safety selectors snicking on and off like butter without so much as breaking your grip. The handguard is relatively narrow, but it’s tall, which some may like more than others. The charging handle is smooth and works well; we appreciate the forward assist feature as well. Our rifle was about a pound heavier than we were expecting based on early prototypes, weighing in at 8 pounds. It’s also longer than you might expect with the stock folded, as the receiver extends back a fair amount from the grip.

Recoil impulse was very soft and more of a shove than sharp. The system is oversized for 5.56, so it wasn’t bottoming out the buffer either. It’s remarkably smooth and easy to run fast and hard.

We had some intermittent feeding issues where the next round would lodge itself at about a 45-degree angle. We tested that same magazine in a standard AR we had on-hand and suffered the same problems, so we deemed it a bad magazine and retired it. The only other issues we experienced were two failures to lock back on empty in the first four magazines we shot through the gun. Beyond that, the UXR was problem-free.

LOOSE ROUNDS

PWS’s UXR is an impressive design feat, chock full of thoughtful and intelligent features. For goodness’ sake, you can remove the trigger pack by pushing a button! Everything is easy to service, maintain, and reconfigure. If you love clever mechanical things, you’ll love the UXR. It’s incredibly smooth, and it’s very accurate. What’s not to like?

Well, it’s a premium product, and it’s not cheap. If you don’t value the modularity and other benefits it provides, you could put your scratch toward a high-quality purpose-built rifle.

But there’s nothing else quite like the UXR. 

Current caliber offerings include .223, .308, and 300BLK, with additional calibers such as 6.5CM, 8.6BLK, 7.62x39mm, 6.5 Grendel, and 6mm ARC planned. Conversion kits will retail at $575 — it’s not that bad once you’ve already bought into the platform to switch so easily from .223 to 7.62×39 or .308. Also coming down the pike are more color options and alternative handguards and stocks.

We’re big fans of the UXR platform. If you’re on the fence about ponying up the scratch for an UXR, consider getting one in .308 — that could be the sweet spot given the pricing of other alternatives. You owe it to yourself to at least take a look. It’ll be hard to resist once you do. 

SPECS:

• Primary Weapons Systems UXR
• Caliber: .223, .300BLK,
• .308 Win
• Capacity: 30 rounds
• Weight: 8 pounds
• Barrel Length: 16 inches
• Overall Length: 34.1 inches
• (28 inches with stock folded)
• MSRP: $2,650

Accessories:

• Vortex Optics Razor HD Gen III 1-10×24 FFP MRAD scope $4,000
• Scalarworks LEAP/09 34mm scope mount $399
• Primary Weapons Systems BDE 762 Suppressor $950
• Wolfpack Armory Low Profile HUB Adapter (Plan B) $70
• SureFire Scout Light Pro Dual Fuel $359

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