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6MM ARC: Long Range in a Small Package with the Lantac 6ARC

The folks at LANTAC first caught rumor of an exciting new round in development for the AR-15 back in 2018. They were part of a military research project looking for both a new rifle and corresponding intermediate caliber. In January of 2019, they were among a small, select group of companies handpicked to further develop the 6mm ARC and the rifle to go with it. Hornady, PROOF, and E-Lander were also a large part of this project.

Once they had their base design with Hornady supplying the ammunition, Lantac decided to invest a lot of research and development on the capabilities of shorter barrels with 6mm ARC. Because some companies actually do the R&D, Lantac started with an 18-inch barrel with an extremely short gas system, then cut off an inch at a time while tracking ballistic results and capabilities. Once they hit the 15-inch mark, they began chopping off a half inch at a time. In particular, we were told that 14.5 inches was phenomenal in terms of increased range compared to its 5.56 brethren.

6mm arc

Left to Right: 300BLK, 5.56, 6ARC, and 7.62N compared.

But they didn’t stop there. Everyone involved was surprised at the capabilities of the 11.5-inch barrel for its size, so they settled on that for a shorty. Thus, the impetus of this article: what we dub the Lantac 6ARC Pig/People Popper.

DESIGN

We should first note that we’re using a preproduction prototype for this review. Some details may change prior to full production, and we’ll note anticipated changes along the way. For the roots of this stubby 6mm ARC, Lantac started with their LA-SF15 UTP LAW Pistol and made modifications from there. You get the same receivers, SPADA-ML M-LOK handguard, LAW folder, and ambi controls; you just get a bit more to top it all off.

lantac 6arc

The base is a Lantac LA-SF15 UTP LAW.

Our version came bundled with the single-stage, 3.5-pound E-CT1 trigger. This co-branded Timney cassette-type trigger delivers a crisp and light break, especially when using the bottom of the bow.

An 11.5-inch 1:7.5 twist PROOF barrel is the heart of this rifle. Even with this diminutive barrel length, Lantac forgoed the traditional carbine-length gas system and went with a mid-length system for a smooth impulse. This is especially impressive when you consider a mid-length gas system can be finicky to dial in even on a 14.5-inch gun, but Lantac consistently uses longer gas system lengths than tradition dictates.

Aside from the caliber itself, the most innovative component here is Lantac’s enhanced bolt carrier.

lantac 6arc enhanced bolt carrier

Lantac has never really made a “standard” bolt carrier group; they’ve always incorporated at least some big upgrades from Stoner’s original design. The heavier Lantac E-BCG for the 6mm ARC is the most advanced that they’ve produced to date. Starting with a billet of 8629 steel, the carrier is machined then coated with nickel boron via the diamond NiB polish process for an extremely slick and slippery result. The bolt is Carpenter 158 and magnetically particle inspected, like we’d expect from any quality manufacturer. As with all other Lantac carriers, the 6mm ARC E-BCG features their domed head cam pin, designed to reduce wear both within the receiver itself as well as the cam-pin track in the carrier itself.

In order to keep gas out of your face, especially when shooting suppressed, Lantac added some additional gas vent holes, some cut at an angle to blow gas forward during cycling. These also aid in keeping the bolt in battery slightly longer, simulating a longer dwell time and allowing for smoother cycling. All said and done, Lantac says their estimated bolt life is three times longer than the current standard-issue bolt.

BALLISTICS

We can’t pretend we haven’t seen intermediate calibers in AR-15s before, like the 6.8SPC, 6.8SPC II, 6.5 Grendel, and more. So, it wasn’t a surprise to learn that the parent case of the 6mm ARC stems from the 6.5 Grendel, which itself is kind of an incestuous mash-up of .220 Russian and 7.62×39. None of those rounds really caught on outside of niche groups and hog hunters, but the backing of several successful companies plus real-world use in the Department of Defense gives us confidence to say this one may break away from the wildcat-cranny into the wider world of shooting.

6mm arc velocity

6mm ARC is initially available in 103-, 105-, and 108-grain loads. Undoubtedly, more will be released as popularity increases in both the public and private sectors.

The most effective demonstration of the ballistic capability of the 6mm ARC is to directly compare the Lantac 11.5 with 108-grain ELD match to the Knight’s Armament 20-inch barreled M110 7.62x51mm sniper rifle shooting 175-grain SMK. The charts speak for themselves:

6mm arc ballistics

Impressively, these two vastly different rifles diverge by no more than about 0.7 mil — and that’s at 1,000 yards. You’ll also note that when shooting the full kilo, 6mm ARC has more velocity than 7.62x51mm.

6mm ARC WEIRDNESS

Magazines may be an issue and are undoubtedly the main issue you’ll hear with initial reviews. While 6.5 Grendel AR magazines could ostensibly be used, we received a pair of dedicated 6mm ARC Israeli E-Lander magazines. While they’re about the size of a 20-round 5.56 magazine, each one holds 17 rounds of 6ARC. Similarly, what appears to be a 30-rounder only holds 24. A cursory examination gives the impression that the 6ARC magazine is no more than a 6.5 Grendel mag with new markings. Time will tell if further refinements will be needed, similar to Magpul tailoring PMags for 300BLK even though that round feeds well from standard 5.56mm magazines, for the most part.

6mm arc lantac enhanced bolt carrier group

The angled gas ports on the E-BCG push gas away from the shooter.

All 6mm rounds suffer from velocity increases during barrel break-in; the 6mm ARC is no different. All told, you’ll have to chew through around 150 rounds before these velocity increases level off, which is why we’re reviewing an already-fouled preproduction barrel. Precision rifle competitor Ryan Hey from MagnetoSpeed explained this phenomenon:

“…a bullet speeds up due to the lands on the rifling being smoothed out as bullets pass over their surface. This increased bearing surface of the bullet increases pressure, thus the increase in velocity. Copper also fills in the microscopic divots in the metal, but the lands being smoothed out has a greater effect.”

Therefore, you should closely track your first few hundred rounds with a new barrel with the aid of a chronograph to determine your ultimate velocities.

OUTFITTING

An easy choice for an optic, even though this is a short barrel, was the Vortex 1-10x FFP. While some would call that overkill for an 11.5-inch rifle, the 6mm ARC is very capable of long-range accuracy, and we’re no strangers to LPVOs on SBRs. For a white light, we fitted the SureFire Scout Pro M640 and SR-07 switch with an Arcane Concerted ARCband for wire management. The M640 features an articulating mount and can be directly attached either to Picatinny or M-LOK handguards. The forward controls are an Arisaka finger stop used in conjunction with a Unity Tactical VFG (converted to M-LOK from KeyMod).

6mm arc outfitted

This isn‘t a precision rifle capable of a combat role. This is a combat rifle capable of precision.

Since we decided on an LPVO for an optic, we ditched the pistol lower and went with a previously registered SBR lower. All of Lantac’s components were successfully transferred to this lower. We tossed the LAW Tactical folder on it but replaced the brace with a B5 Systems SOPMOD stock.

While the Lantac comes equipped with a regular .30-caliber Dragon muzzle brake, we swapped it for a Dear Air and KeyMo compatible Lantac muzzle device. Any Dead Air rifle can drops right on, as will any suppressor with a universal HUB 1.375×24 rear-end combined with a KeyMo adapter. Any silencer with 1.375 HUB mount gives you dozens of device options right from the gate.

We added a pair of Magpul MBUS Pro BUIS, because even in 2020 we still need BUIS to avoid ridicule on the internet.

Once we got our sights, optics, and controls sorted out, it was time for the range.

AT THE RANGE with 6mm ARC

Sometimes a particular combination of ammo, muzzle device, and silencer gave us good results, and other times the opposite; at first, we thought we were dealing with strange barrel harmonics. Ultimately, we found it to be a heat issue. From a cold bore, we’d get sub-MOA groups (just under 0.9 MOA), which would open up to nearly twice that once the barrel was heated over the course of two magazines. Keep in mind that this is a pre-production barrel, and the variation may not be as drastic with production models. Also remember this gun isn’t intended for PRS competitions but to replace 5.56mm — even our largest groups were smaller than standard M855/A1.

LAW Tactical Folder 6mm arc

The LAW Folder allows for an extremely portable package.

We tried out several silencers, settling on the Dead Air Sandman-S with a 7.62 flash hider endcap. Not only did it consistently group well, the shift when attaching the silencer was exactly 1 mil low, making for incredibly easy adjustments when popping small targets at range.

We found it simple to engage MOA targets out to 800 yards. After it goes transonic, projectile flight becomes erratic. Still, we got hits on a 12×12-inch plate at 1,000 yards, with the main limiting factor being the center aiming point of the Vortex 1-10x reticle obscuring a target of that size.

6mm arc color build

This isn’t a precision rifle capable of a combat role. This is a combat rifle capable of precision.

LOOSE ROUNDS

If the 6mm ARC doesn’t put the NATO 5.56 on life support, it won’t be because the 5.56mm is better, but because Hornady simply doesn’t currently have the machines to produce 6mm ARC in quantity — all the machines are running 5.56 and 9mm around the clock to keep up with the never-ending pandemic and pre-presidential panic. In every measure of capability, sans magazine capacity (which is being addressed as we type these words), the 6mm ARC totally beats the pants off of everything available that fits within the confines of a standard AR-15 footprint. 900 yards before transonic with a short barrel? 5.56 eat your damned heart out.

 


More on 6mm ARC, and from LANTAC

  • San Tan Tactical, Hornady, Proof Research Team Up for 6mm ARC Release with STT-15 Rifle. Read Here.
  • LANTAC's Enhanced BCG is now available in Black Nitride.




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