Everybody knows that modern sporting rifles on the AR-15 platform are some of today’s most popular firearms. A lot of companies make them, and they come in all sorts of versions and chambered for many different cartridges.
The new LAR-15 Lightweight Mountain Rifle from Rock River Arms is opening up new ground for the AR-15.
Rock River Arms Inc. (RRA) is an innovative firm founded in 1996 by brothers Mark and Chuck Larson and is headquartered in Colona, Illinois. After stints at Springfield Armory and Les Baer Custom, the Larsons had considerable expertise in the construction of high-quality guns, and in 1993 they were building AR-15s for Eagle Arms in Coal Valley, Illinois.
At about that time, they formed their own company called Tolerance Plus, which was later changed to Rock River Arms. (For anyone not familiar with Illinois geography, the Rock River runs alongside Colona.)
RRA also makes many versions of high-quality Model 1911 pistols, and Shooting Times has reviewed several of them over the years.
ST has also reported on RRA’s fine AR-15s. Speaking of that, some of RRA’s unique ARs include models chambered for 6.8 SPC, .300 Blackout, .458 SOCOM, 7.62×39, 7.62 NATO/.308 Winchester, plus others in pistol calibers like 9mm and .40 S&W.
RRA builds left-hand models, too, and the firm makes piston-driven ARs and sells gobs of individual parts.
The bulk of RRA’s AR production is in 5.56mm/.223, the most popular cartridge of the bunch. The new Lightweight Mountain Rifle (LMR) is chambered for 5.56, which means it will also accept the .223 Remington round. The new LMR shows considerable sophistication and quality in its features.
At first glance, this sleek little gem appears smooth and clean-cut; it doesn’t have a lot of projections or add-on parts sticking out here and there. You can add them later, if desired.
The grip and handguard are comfortable, and the carbine just feels “right” the minute you pick it up. At a svelte 6 pounds, 6 ounces, it is a comfortable carry.
The LMR has a standard gas-impingement action and a 16-inch lightweight chrome-moly barrel. The twist rate is 1:9, and it will accurately stabilize bullets up to 69 grains with ease. The lower receiver is a forged LAR-15, and the upper receiver is a forged A2.
The flat-top upper is festooned with plenty of cross slots for a traditional scope mount or an ACOG. Up front, the muzzle is threaded 1/2-28, and the LMR comes standard with an A2 flash hider. One 10-round D&H Industries magazine is provided, but, of course, it will accept standard, higher-capacity magazines, too.
The trigger is RRA’s two-stage unit, and the pull weight on my test rifle averaged 5 pounds, 11.5 ounces. It was smooth and crisp.
The LMR also features RRA’s proprietary lightweight low-profile gas block, which is concealed by a lightweight 12.75-inch aluminum handguard that is specifically designed for the gun.
The handguard is devoid of sharp-edged lumps and bumps that make for an uncomfortable handhold.
Atop the handguard is a full-length Picatinny rail that is attached by three hex screws on each side. The rail has slots its entire length so that BUIS, a flashlight, a laser, or a scout scope can be easily mounted. The buttstock is RRA’s six-position adjustable CAR stock, and the excellent Hogue pistol grip comes standard.
In addition to the magazine, the LMR comes with a detailed owner’s manual; an LPS-1 Weapon wipe; and a lockable, foam-lined, hard plastic RRA case.
RRA claims “1 MOA accuracy at 100 yards,” so I was itching to give the little carbine a workout on the range and see if the statement was fact or just hype. I used a new Burris Predator Quest 2-7X 35mm scope in a Burris one-piece P.E.P.R. (Proper Eye Position Ready) scope mount.
Especially made for flat-top ARs, this mount provides great flexibility on positioning the scope for proper eye relief. Two sets of ring tops come with the mount.
One pair is smooth on top; the other pair has Picatinny slots for the attachment of a dot sight, a laser, or other doodads. The Predator Quest line was introduced last year, and in addition to the 2-7X 35mm, there’s a 3-9X 40mm and a 4.5-14X 42mm in the line. All are matte black, and the latter two scopes are also available in camo finish.
The Predator Quest line has Burris’s Ballistic Plex E1 reticle, which is interesting. It seems to “float” in space, as the ends of the crosshairs do not go to the edge of the field of view.
The lower vertical crosshair has hash marks of varying widths that allow for a measured holdover. Dots at each end of the hash marks show the approximate wind drift for a 10-mph breeze with typical high-velocity varmint loads. The crosshairs are fairly thin, and while this reticle is great in good light, it’s hard to see in low light.
The optics of this little scope are top drawer, bright and clear edge-to-edge, and the adjustments work well. It has 1/2-minute click adjustments, instead of the more common 1/4-minute, but I think that’s perfectly adequate on a lower-powered scope like the 2-7X.
Before shooting, I cleaned the LMR’s bore really well and took a peek at it with my Hawkeye borescope. The chamber and rifling were smooth and slick, and the gas port didn’t have any burrs sticking out around it.
I did a little quasi “barrel break-in” by shooting several full magazines for functioning and then cleaned the barrel thoroughly after every 10 rounds with Butch’s Bore Shine and Otis O12-CU Copper Solvent.
I had many different .223 factory loads on hand, so I tried almost all of them. Some may question why I shot so many loads in the LMR. The answer is simple: Just about every load shot really well in it, and I was having too much fun to quit!
Every load but one (Federal’s offering that’s loaded with the Barnes 55-grain TSX Bullet) shot close to an inch at 100 yards. It didn’t seem to matter what the bullet weight was; they all shot about the same, with that one exception.
Short barrels reduce velocity somewhat, and the average velocity of the factory loads out of the LMR’s 16-inch barrel was 12.3 percent below the speeds listed by their manufacturers.
The best load in the rifle was the Federal 62-grain Fusion load. It clocked 2,642 fps and had a group average of 0.70 inch. One group with this load measured 0.43 inch! If this was my rifle (and there’s a good chance it will be), I’d stock up on this Fusion ammo and live happily ever after.
The average of all 12 factory loads I test-fired was 1.08 inches at a measured 100 yards. If the TSX load is excluded, the average of the remaining 11 loads was a tidy 0.99 inch.
The results with the Barnes bullet were surprising, as I have used it in numerous rifles, and it has performed well. It’s a game-getter, and I can report that it will shoot through a 300-pound hog, side to side, and exit.
But as we know, rifles are individuals.
I had to try a few handloads, but after the stellar results with factory fodder, I didn’t knock myself out with the reloads. The five handloads I fired used typical 50- and 55-grain varmint bullets, and they averaged 1.04 inches, besting the factory ammo by a smidgen.
The overall combined group average of factory ammo and handloads was 1.07 inches. Technically, MOA is 1.047 inches, but in my book 1.07 is close enough to call the LMR a true 1-MOA gun.
I’ll add that the LMR was 100 percent reliable. All factory ammo and handloads fed through the magazine, without a single malfunction of any kind.
It will come as no surprise that I am not a huge fan of ARs, generally, but I like accurate, reliable rifles that are pleasing to the eye and hand. So I have to admit that the RRA Lightweight Mountain Rifle is a darn nice gun.
It is aesthetically pleasing, functions perfectly, and shoots better than at least 75 percent of the bolt-action sporters I’ve wrung out over the years. Oh, yeah, it’s pleasantly lightweight for an AR, too.