October 02, 2023
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Rock River Arms has introduced a new line of AR rifles, the Operator DMR (Designated Marksman Rifle). There are two versions chambered in 5.56 NATO, and four in .308 (7.62x51 NATO). Later on in this article, I want to explore exactly what a “designated marksman” is, and what kind of rifle they might use, but here, I will quickly say that it is a military term which indicates a skilled shooter using an accurized or enhanced rifle that can bridge the gap between a standard service rifle and a dedicated sniper rifle—which should give you a little clue as to what kind of rifles these are. Both the 5.56 and .308 versions are offered with 16- or 20-inch barrels, and I secured a sample of the 20-inch 5.56 Operator DMR for testing. Before I dive into the specs of this 5.56 version, let me talk about the .308 models. The .308 Operator DMR uses billet receivers, and is offered with a 16- or 20-inch barrel. Rock River Arms (RRA) also offers two additional .308 models which are identical to the above two except for the addition at the factory of a SilencerCo Chimera 300 suppressor (requiring additional unconstitutional NFA paperwork/processes for purchase). The 5.56 model is not offered from the factory with a suppressor, and I suspect this is because there are so many great 5.56 suppressors out there—far more than .308 cans. Whatever 5.56 can RRA chose, a big percentage of their potential customer base would probably want something different….
The 5.56 version of the Operator AR is technically the Rock River Arms LAR-15M Operator DMR. Rock River first introduced their Operator series in 2022, and those rifles are meant to follow the “everything you need and nothing you don’t” philosophy in rifles meant for self-defense and law enforcement
applications. The DMR series offers different features, including longer barrels. A 16-inch AR is the most common type found in this country, because it does everything well. However, there is a definite velocity loss when compared to a 20-inch barrel. That won’t make much if any difference at urban distances, but as a DMR is meant to be able to perform at range, offering a 20-inch variation is smart. Longer barrels are not automatically more accurate, but the (roughly) 100+ fps increase you get out of a 20-inch barrel might make all the difference at range.
The 20-inch chrome-moly vanadium barrel on this rifle has a phosphate finish and what I’ll call a medium-heavy contour. The barrel is the single heaviest part on an AR-15, and this beefier tube means this rifle has an unloaded weight of eight pounds, three ounces, including the provided sights (which I’ll get to in a bit). With a magnified optic mounted, a loaded magazine inserted, and the stock properly positioned, this rifle will be 40 or so inches long and 11 pounds or more—significantly longer and heavier than an M4, but lighter and shorter than any type of dedicated sniper rifle. Shorter barrels are often more inherently accurate, because they are shorter and proportionately thicker, thus stiffer and providing less flex. Manufacturers add weight to rifle-length barrels for several reasons—it makes them stronger, so there is less flex, increasing accuracy. The added metal acts as a heat sink, which means they take longer to heat up. There are always zero shifts (point of impact changes) between cold and hot barrels, but a thicker barrel means this will take longer, and/or the shift will be less.
The barrel sports a 5.56 NATO chamber, which means it will handle .223 Remington and hotter 5.56 NATO ammo equally well. It is chrome lined, with a 1:7-inch twist and a rifle-length gas system. With a 20-inch barrel and a designated marksman rifle it is assumed you’ll be using heavier bullets more often than not, for improved performance at distance, and the fast 1:7-inch twist rate helps to better stabilize those long heavy bullets.
A Family History That Includes the DEA
I find RRA’s barrel choice interesting. Chrome-lined barrels are generally thought to be less accurate, but the military specs that for their barrels because of how much more durable they are. There’s nothing better for resisting corrosion. RRA does do some law enforcement sales, and I bet the chrome-lining on a barrel is more important to potential police department purchasers than accuracy. That said, commercial barrels (chrome-lined and otherwise) are far more accurate than what you find in the average military rifle. Combine that with the fact this barrel is free floated inside the handguard, plus having tested more than a few RRA rifles over the years and knowing their capabilities, and I was expecting more than acceptable accuracy.
And a brief aside, to talk about Rock River Arms’ history with law enforcement sales, as it’s very pertinent: way back in the previous century Rock River Arms (RRA) decided to expand from making well-respected 1911s to AR-15s. This was before the modern black rifle boom, back in the era when there was Colt, and then there was everybody else. Nobody paid much attention until one of RRA’s rifles was adopted by the Drug Enforcement Administration to replace that agency’s aging Colt 9mm SMGs. That wasn’t just a press release with no substance, they were actually issued to street agents en masse as the concept of .223 “patrol rifles” caught on with American law enforcement. A close friend of mine, who is still with the DEA and one of the top-ranking guys there, soon to be forced into retirement as he’s got over 30 years on the job, was issued one of the RRA ARs. While large police departments and federal agencies tend to favor Colt and Daniel Defense, a lot of smaller departments still remember that DEA contract and buy duty rifles from Rock River, as they are still going strong, and the DMR is built as much for them as it is the private citizen. In a volatile market that has seen huge ups and downs, Rock River Arms has, for decades, remained one of the most successful manufacturers producing AR-15-style rifles in the country.
The barrel of the DMR is threaded 1/2x28 and tipped with a standard A2 flash hider, and the gas block is a low-profile model under the handguard secured with two set screws. The barrel freefloats inside a 17-inch aluminum handguard of RRA’s design that sports M-LOK compatible accessory rails at 3, 6, and 9 o’clock. The aluminum handguard sports steel tabs at the back which slide over the upper receiver and keep the handguard from rotating. Long and somewhat narrow aluminum handguards are in style. They provide a lot of gripping area, and you can get your hand out closer to the muzzle to better muscle the gun from target to target. They also provide a lot of mounting area, and I can see this rifle sporting a bipod if actually put into use as a DMR.
The rail slots in the upper receiver are T-marked, but the ones in the handguard are not. Marked slots are useful when detaching and reattaching gear, to make sure you’re putting it back where it was. I don’t know how often the average person will need that, but having the receiver so marked, and the handguard not, looks wrong to me. The Operator DMR ships with a set of Magpul Pro-Series steel MBUS flip-up sights, which I wholeheartedly support. Every firearm meant for serious use should have iron sights, and on a rifle marketed to private citizens and law enforcement as having everything you need and nothing you don’t, iron sights are a must have. Scopes break, and batteries die, but if you’ve got iron sights you can still use that rifle as a rifle, rather than a club or a cane. With the long barrel and handguard on this rifle, the distance between the front and rear sight is about 21.5 inches, providing more than enough precision to engage targets out to the limit of your ability. The Magpul rear sight has two apertures and click adjusts for windage using a thumbwheel (that was very stiff). The front sight has Magpul’s very fine match post which measures 0.04-inch wide is click adjustable for elevation again using a stiff thumbwheel. When folded down they lie very flat to the rifle. These sights sold separately are $210.
RRA also includes a QD sling swivel socket that attaches to an M-LOK slot. When combined with the sockets and slots on the stock you can mount a sling to the rifle without having to buy any additional hardware, which is nice. The rifle also ships with a five-slot Picatinny rail to mount to the handguard (for foregrips/lights/etc.). The upper and lower receiver are standard forged units, with the expected GI features—a traditional case deflector and forward assist, ejection port cover, and MilSpec bolt and magazine release. You’ll see the RRA Operator name laser-etched on the right side of the magazine well, and on the left side you’ll see the standard RRA logo plus the model marking (LAR-15M) and the serial number.
On the left side of the lower receiver you’ll see Rock River’s well-known Star safety selector. The end of the safety lever has a raised, serrated dome that rotates under your finger as you work the safety. In truth, I love the way this selector works, but hate the way it looks. The pistol grip is a Hogue rubber overmolded model with finger grooves and a beavertail to add more material under the web of your hand. It does not have a storage compartment in it. Personally, I don’t care for rubber grips on ARs as the rubber tends to grab my thumb when I’m trying to work the selector—but that’s a personal preference, not a complaint. The trigger guard is an oversize RRA aluminum model that pivots down a little bit if you’re wearing gloves that require even more room. The charging handle is a RRA design and features their extended latch. This ribbed latch extends quite a bit on the left side compared to the small GI piece, making the handle much easier to work.
Inside the lower receiver is RRA’s two-stage National Match Ultra Match trigger. This differs from RRA’s well-respected standard two-stage trigger. It provides the same 4.5 to five-pound pull, with full-power springs, but the components of the Ultra Match are wire EDM machined. My sample had a light, short takeup, then a very crisp break, and a total pull weight of 4.5 pounds. In my opinion, perfect for a DMR rifle. At the rear of the rifle is BCM’s original carbine stock. It has a slot and QD sockets for mounting slings, and a non-slip rubber buttpad. The stock has an enlarged SOPMOD-style cheek section for more comfortable shooting. It rides on a six-position buffer tube. The Operator DMR uses a standard carbine buffer. Supplied with the rifle is one 30-round polymer magazine. They are marked with the Rock River Arms name, but I assume they are rebranded IMI Defense G2 mags as they are identical. They have a non-tilt follower and a dot matrix on the sides if you want to mark your mags. Before I dive into the scope I chose to use to test this rifle, I think we need to ask (and answer) the question:
What’s a DMR?
There is no one universal definition as to what constitutes a sniper rifle, or sniper, for that matter, and the same holds true for a designated marksman or a DMR rifle, although the term does have a military origin. In general, a designated marksman (occasionally called a sharpshooter) was meant to provide
accurate fire at ranges in excess of what a soldier with a standard service rifle was capable of, but not out to the ranges a true “sniper” was able to perform. To accomplish that, he used a rifle a step up from the standard piece. Sometimes a DMR was simply a standard service rifle with a magnified scope mounted atop it, and the person using it had little to no training, but was instead given the job because they had proven themselves to be a good shot. Snipers use specialized rifles and go through training to hit targets at ranges beyond the capability of the standard soldier and his rifle. They are also trained in fieldcraft, stalking and surveillance. Designated marksmen are usually just given additional marksmanship training. Sometimes, as I said, there’s not time or money to provide additional training, and the DM role (and rifle) are given to the soldier who has proven himself a good shot.
However, in reality, there is always a huge amount of overlap. Most “sniping” is done at quite short distances—the average police sniper shot is just 77 yards, and most shots taken in Iraq were in urban environments, well inside 500 yards. An AR-15, loaded with the right ammunition, works very well out to 500–600 yards. And by right ammunition I don’t mean accurate ammo (although that’s a must), I mean ammunition that is loaded with bullets that still have the energy to get the job done at distance. The 77-grain Mk262 Mod 0/Mod 1 cartridge was specifically developed because the issue 62-grain military 5.56 ammo had poor accuracy and very little terminal effectiveness at the extreme ranges seen in Afghanistan. This purpose-built ammunition extended the range of the M4 and the DMRs, such as the MK12 SPR, fielded overseas. Generally, DMRs are chambered in a cartridge commonly found in the military (5.56, .308), so if the user runs out of specialty ammunition, they can make do with standard issue ammo.
The advantage of a heavy caliber dedicated sniping rifle is most often seen at extreme distance, where the bigger bullets of the 7.62x51, .300 WinMag, .338 Lapua, and .50 BMG buck the wind better and have enough horsepower behind them to drop bad guys. But quite often those guns are long, heavy bolt actions, and perhaps not what you want or need when you’re working in urban environments, dealing with multiple bad guys. That’s where the DMR shines. DMRs have included everything from M-16s mounted with 4X Trijicon ACOGs to various versions of the M14s (M21, M14 EBR, etc.). The Mk 12 SPR is a purpose-built DMR, scoped, suppressed, accurized 5.56 AR, that was used to great effect in Afghanistan. Accurized big bore semi-auto rifles like the American .308 M110 SASS and the Soviet 7.62x54R SVD (Dragunov) hover somewhere between DMRs and sniper rifles. You can start arguments talking about them with purists, who feel no semi-auto rifle should be considered a “sniper rifle.”
At the Range
For testing I needed a scope that fit with the intended use of the Operator DMR, and chose the new Mark 5HD 2-10X from Leupold. This medium-range magnification tactical scope seems a perfect choice for a DMR rifle, and look for a separate write-up of this scope soon. For my accuracy testing, I simply had to include Black Hills’ Mk262 Mod 1 ammunition. This ammunition was developed in concert with the Mk 12 SPR for Afghanistan. The Mk 12 SPR is, by any other name, a DMR, and the military wanted ammunition for it that performed better, at distance, than standard military ball. The end result was the Mk 262 ammunition, later incrementally improved to the current Mod 1 version. This ammunition features a Sierra 77-grain OTM bullet—renamed from BTHP (boat-tail hollow point) to OTM (open tip match) because the military doesn’t like the phrase “hollow point,” even though the cavity in the tip is not designed to expand. This ammunition is built to exacting standards and will generally do under 0.7 MOA out of match barrels, and was intended to engage bad guys in Afghanistan out to 700 yards. This ammo wasn’t just more accurate—the terminal performance of this ammunition was so much better than the 62-grain “green tip,” at every range, that anyone and everyone who could get it loaded it into their M4s. Upon impact the long bullet will generally yaw. The tip will break off, and usually the bullet will snap in half at the cannelure, forming two or three different wound tracks.
Black Hills sells 460-round ammo cans of this ammo as their Mk 262 Mod 1-C MIL-PACK. The only difference between this ammunition and what they supply to military special forces is the military ammunition is loaded onto stripper clips. Out of a 20-inch barrel it will do over 2,700 fps, and the great ballistic coefficient of the bullet, combined with its heavier weight, drastically extends your range when compared to traditional .223/5.56 loads. At the range the Operator DMR averaged just under 1.0 MOA between all the loads tested, which is more than acceptable for a duty-grade chrome-lined barrel. The rifle (no surprise) seemed to prefer the Black Hills Mk 262 Mod 1-C, and it would do roughly 0.8 MOA with that ammunition. With other quality ammo it would do 1.0 MOA and under, and even bulk-class FMJ did respectably, printing 1.5 MOA groups.
I did groups on paper out to 100 yards, and clanged steel out to 200 yards, but this rifle is capable of reaching out much further than that. Between the weight of the gun, scope, mount, and loaded magazine, there was—as expected—very little recoil. Off the bench the rifle gave a little nudge back into the shoulder, but there was no muzzle rise. Shooting off the shoulder was just as pleasant, although you do start to notice the weight pretty quickly. Rock River Arms is perfectly capable of building a match-grade AR capable of half-MOA groups, but you’d definitely pay for it, and that’s not what this rifle is. The Operator DMR is meant to provide better than average accuracy with a barrel that’s ready for duty—it’s got the more forgiving 5.56 NATO chamber and a chrome-lined bore that will handle abuse as well as anything. The 20-inch barrel will maximize your velocity. As promised, it delivers everything you need and nothing you don’t, at a price you can afford.
Rock River Arms Operator DMR LAR-15
- Caliber: 5.56 NATO (tested), 308
- Weight: 8 lbs., 3 oz.
- Overall Length: 36.5 in. (collapsed), 40 in. (extended)
- Upper: Forged 7075 T6 aluminum
- Lower: Forged 7075 T6 aluminum
- Barrel: 20 in., 1:7-in. twist, rifle-length gas system
- Muzzle Device: A2 flash suppressor
- Sights: Magpul Pro flip-ups
- Trigger: RRA Two-stage Ultra Match, 4.5 lbs. (tested)
- Buttstock: BCM
- Pistol Grip: Hogue rubber overmolded
- Handguard: 17 in. Free-float aluminum (M-LOK)
- MSRP: $1,765
- Contact: Rock River Arms
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