Author sends rounds downrange with Rock River Arm’s awesome Operator DMR.
Rock River Arms has remained a trusted name in the expansive world of AR-type rifles over the years, largely for the rock-solid reliability of their products (yes, I said rock) and the incredible accuracy of their barrels/rifles. We have reviewed a couple of Rock River Arms (RRA) products over the years and have been impressed with the performance that RRA delivers. We have been waiting for several months to secure a LAR-BT3 Operator DMR 20” in .308 Winchester for review and the wait was worth it.
Ok Mr President, if you need to send me to Iran because you desperately need old Aerospace Engineers, I will go. But I insist I get to bring my own rifle.
RRA’s traditional AR-10 type rifle, the LAR-8 was always a solid performer and, surprising no one, earned a reputation as an incredibly accurate rifle. It uses LAR-type magazines, and they are no longer as plentiful nor as cheap as they once were. RRA also developed the LAR-BT3 which had some design changes from the LAR-8 including use of SR25 type mags (think PMAGs). This appealed to me as I have a Ruger SFAR and a lot of 20 round PMAGs. Commonality of parts and all…
The LAR-BT3 Operator DMR is designed as a rifle that is ready for a rough life in harm’s way. The chrome-lined barrel, the back-up sights, the crisp match trigger and the boron-coated bolt carrier group all combine to make a ruggedly accurate weapon. The barrel profile is not a pencil thin sporting weight barrel, but it’s no bull barrel either. It strikes a compromise that favors light weight for handiness and yet provides for multiple precision shots, even in hot environments.
The Rock River Arms LAR-BT3 Operator 20” DMR
Another excellent design choice that RRA made is the decision to keep all ambidextrous stuff off the rifle. Nothing against my south-paw friends but, you adapted to the M-16 for the last 60 years, I have faith you can shoot this weapon well.
Test Shooting Phase
The Operator DMR features a profoundly extended charging handle release that I grew to love during shooting sessions. The charging provides the operator with a good grasp even with a large eye piece optic installed. Also worth noting is the Operator ships with a 20-round mag, and spare Magpul MLOK QD mounts. I ended up using a 10-round PMAG for bench shooting.
Not sure how this is possible, but I was routinely shooting roughly the same sized groups at 200 yards that I was shooting at 300 yards. I think my range is cursed.
I field stripped the weapon before shooting and wiped the preservative off all the internals and ran a couple patches through the bore. The BCG got a good coating of CLP before denting primers.
Oddly for me, I did not zero the excellent Magpul MBUS Pro sights. I mounted a trusty old Leupold MK4 4.5-14X LR/T scope–that is usually at home on my 35-year-old Fulton Armory M14NM–on MK4 high rings and this optic remained in place for all of my testing.
I’ve been looking at targets for 20 years though that Leupold glass.
To wring out every drop of accuracy from the Operator, I installed a Magpul Precision Rifle Stock lite and a Timney AR Pro drop in trigger. The BCM collapsible stock installed on the Operator was actually pretty tight, but the PRS lite took every iota of play out of the picture. Likewise, the Operator comes with an excellent trigger that would be fine for its intended use. But the Timney AR Pro trigger is a sweet two-stage trigger with the final pull measuring a mere 1.5 pounds. Plus, the Timney took literally 5 minutes to install. It’s an incredible trigger. If you haven’t installed a Timney drop-in AR trigger in a while, good news, their new triggers no longer use set screws. Just tighten two screws on the trigger and hammer pins and you’re done!
Did we need an awesome trigger for this review? NEED is a funny word. Yes, yes we did! Rock River Arm’s trigger was really good. But I wanted to see how the Operator would group with a 1.5lb trigger.
Also, for this testing I used the excellent Athlon Rangecraft chronograph to provide all manner of velocity data (see sidebar article on the Athlon).
The Athlon Radar Chronograph is way cool. It will blue tooth to an app on your phone allowing you to revtrieve data etc. It will get a lot of use in future reviews.
I tested with 147 gr PMC XTAC 7.62 NATO, 147 gr MEN German ball 7.62 NATO ammo, 168gr PMC XTAC Match .308, Federal Gold Medal 168gr .308, Hornady 155gr American Gunner .308 and Hornady 168gr AMAX Black .308. I will admit I shot this rifle a lot. I ended up shooting north of 480 rounds for this evaluation. I experienced zero malfunctions of any kind while testing. The rifle was thoroughly cleaned twice during testing.
The RRA Operator DMR fitted with a Magpul PRS lite and a Leupold MK 4 LR/T. Looking for adventure and whatever comes our way.
As it happened, much of my testing occurred during an extremely hot stretch of July weather. All the days I had to shoot the Operator were in the 100+F heat index days. I tried to get out to the range as early as possible for testing as by mid-day my shooting ability was compromised.
Check out that charging handle catch! Oh man. You can hit that even with a large eyepiece scope!
During bench rest shooting, I noted the rifle deposited 90% of the brass right out at 3:00 o’clock (that’s the only AR10 I’ve seen do that!) While the Operator uses a non-adjustable gas block, I would say to not worry as it appears to be perfectly gassed.
Accuracy Results
As expected, the Mil Spec 7.62 XTAC and MEN ammunition both worked smoothly and was nothing to write home about with respect to accuracy. The MEN ammunition averaged just at 2 MOA at 100 yards and the XTAC averaged around 3 MOA at 100 yards.
The PMC XTAC 168gr BTHP acquitted itself well.
Also, not surprisingly, the Federal Gold Medal and the Hornady American Gunner ammunition stole the show at the range. At all ranges, including some amazing 3-shot groups at 300 yards, the Federal GM and the Hornady American Gunner ammo led the way.
Hornady American Gunner .308 155gr ended up taking the accuracy crown. The Federal Gold Medal Match ammo was a very close second.
The Hornady Black 168gr AMAX also performed well out to 300 yards and would be perfectly suitable for use in the Operator. It averaged 3-shot groups of 1.45” at 100yards and acquitted itself well out to 300 yards.
Hornady’s 168gr AMAX Black ammo shot several MOA groups at 300 yards.
The PMC XTAC Match 168gr BTHP did not perform as well as I expected. I’d had fair luck with the XTAC Match in other rifles, but it performed only OK in the Operator.
We used a number of different types of ammo for this review. No malfunctions.
With the Fed Gold Medal and the American Gunner ammunition, the RRA Operator averaged 3-shot groups of 1.23” and 1.15” respectively, at 100 yards, and this carried out to how it performed at 300 yards. I was able to shoot multiple strings of sub-2.5” groups at 300 yards, but on average, I was scoring 3.5” groups. This is impressive accuracy given the barrel profile, the chrome lining and the mission of this design.
Some very accurate groups at 300 yards! It’s true that these groups were the exception not the rule, but how cool is it to shoot three shots in under an inch at 300 yards. That was the one and only group that went under 1” at 300 yards. Holy cow. I put a lot of stock in 300 yard groups.
Rock River Arms LAR-BT3 .308 Operator DMR 3-shot group 100-yard Accuracy Table
.308 Ammunition
Avg Muzzle Velocity (FPS)
100 Yard 3-shot group Avg (Inches)
.308 Hornady 155gr American Gunner
2590 fps
1.15”
.308 Hornady 168gr Black AMAX
2535 fps
1.4”
.308 Federal Gold Medal 168gr Match
2550 fps
1.23”
.308 PMC XTAC Match 168gr
2540 fps
1.9”
7.62 PMC XTAC FMJ 147gr
2731 fps
3.1”
7.62 MEN Military FMJ 147gr
2761 fps
2.2”
I never think 100 yard groups tell the whole story when it comes to accurate high-power rifles shooting high BC bullets.
At the end of testing, I restored the rifle to factory configuration and noted that accuracy really didn’t suffer very much. With the Magpul stock mounted however, I am confident I could use the Operator as a bat and beat a man to death with it, and it would still function properly. For bench shooting I did prefer a full stock and a superb trigger. If I was using this rifle for what it is intended for, the stock trigger is awesome!
35 Years ago, Chrony offered to keep me in chronographs for use in my gun reviews. Over the years, I used their products for hundreds of reviews. They were very supportive and I sincerely appreciated it. I was sad when I learned they were no longer in business.
As I looked around at the next gen chronographs, a radar unit made by Athlon caught my attention. Imagine using a radar unit that you set up behind the muzzle out of harm’s way and doesn’t care about the lighting! Even better, Athlon’s Rangecraft Chronograph records an entire shooting session, to provide reloaders and accuracy nuts with valuable data. Even more remarkable, it will bluetooth to a phone for super flexibility.
In Athlon’s words, “Athlon makes ballistic calculations effortless with the Rangecraft Velocity Pro Radar Chronograph. Using Doppler radar, it tracks your projectile without attaching anything to your barrel—so it won’t change your zero or disrupt barrel harmonics. That means you can test loads and confirm real-world velocity while keeping the same accuracy you trust on target.
Because it doesn’t rely on muzzle blast to trigger, the Velocity Pro reliably captures shots from suppressed rifles and firearms equipped with muzzle brakes, compensators, and other muzzle devices. And with a wide measurement range of 65 to 5,000 fps, it’s built to handle everything from low-velocity projectiles to high-speed rifle rounds—giving you dependable data across a massive variety of setups.”
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