It was the Special Forces need for more power and penetration that became the inspiration for the development of the .458 SOCOM cartridge. Firing a projectile twice the diameter of the 5.56 NATO round and churning up more than twice the energy, the new cartridge was designed to function within the parameters of an M-16/AR-15 operating system. Now Rock River Arms (RRA) has started production of their LAR-458: a factory-produced carbine packing the punch of the mighty .458 SOCOM.
Let’s put things in perspective. We all know about the .45-70 that our great grandfathers used to take down buffalos. Remington currently loads a 300-grain JHP bullet with a velocity of 1810 feet per second (fps), which generates 2182 foot-pounds of energy (fpe). The big frontal area of the bullet combined with its velocity made it a devastatingly effective round on game and human alike. But guess what?
The .45-70 actually produces 10 percent less energy than the .458 SOCOM. If you’re up on your ballistics, you’re saying so what? That’s the same energy level as the .308 Winchester or military equivalent: the 7.62×51 NATO. Knight’s Armament, DPMS/Remington and Armalite all offer .308 rifles built on an AR platform. The difference here is that RRA builds this gun without increasing the size of the carbine.
Measuring just 36.5 inches long and weighing 7.6 pounds, the new LAR-458 packs a big punch for such a small package. In addition to its size/weight efficiency the carbine boasts excellent cosmetics, reliability and accuracy. My test sample possesses a 16-inch barrel and has a flattop receiver for greater versatility of sighting options. But what surprised me was that for a gun chambered for a cartridge so much more powerful than we typically see in this size platform there are surprisingly few modifications that need to be made to the weapon to transform it into a potent thumper.
The .458 SOCOM is a fat, slightly tapered round that possesses a shoulder, which it headspaces on and a heavily rebated rim. The casehead diameter is approximately 0.472 of an inch, or the same as a 7.62 NATO round and its diameter requires that the bolt face be relieved to accept this round. Cursory examination of the bolt carrier reveals that it is a standard carrier. In fact, even the buffer looks to be a normal 5.56 buffer.
RRA does, however, use a heavier than standard buffer spring. Two extra springs were included with my test gun. My carbine arrived with a fixed A2-style stock in place; however, a standard collapsing buttstock can be easily retrofitted to the LAR-458. The CAR spring designed for the collapsing stock has 38 coils and its end is colored red to differentiate it from the longer spring with 42 coils, colored green to be used with the A2 stock.
I wasn’t able to find anything different about the lower receiver. Made from the same aluminum as the rest of their 5.56/.223 rifles, it is hard coat anodized and built to the same specs. That wasn’t so much of a surprise, since the cartridge was literally backed into the M-16 system. In fact, the concept was to build an upper that would fit on any M-16 lower to transform it into a hard hitting, bone crushing machine.
RRA also makes a conversion kit for the .458 SOCOM that includes a complete upper with bolt carrier and charging handle included. That makes a lot of sense for those that need the power of the .458 SOCOM but don’t want to buy another complete rifle. Included with the conversion kit are the two different buffer springs.
RRA engraves the legend, “.458 SOCOM” over the ejection port of their carbine for immediate user identification. Though the ejection port is larger to accommodate trouble-free ejection of the larger casing they are still able to use a standard size ejection port cover.
A heavy barrel, measuring 0.928 of an inch in diameter, is used on the SOCOM and it is threaded at the end to accept a flash hider. My sample wore an A2-style flash hider, obviously modified for the larger bullet, but the rifle is available with a Smith Vortex flash hider. RRA rifles their chrome moly barrels with a 1:14-inch twist to stabilize the big, heavy bullets.
An unmodified direct gas impingement system is used to cycle the SOCOM carbine. It is the same system used on standard M-16/AR-15 rifles. Its barrel is free floating and an aluminum handguard is used on the SOCOM. Its small diameter makes it comfortable in my hand – far more so than the bulky M4 handguards. The gas block has a railed top to accommodate a detachable iron front sight.
RRA ships the rifle with one 5.56mm 30-round magazine. Also accompanying the rifle was an instruction card that details how to bevel the front edge on the magazine for optimal performance. However, I used a number of other standard M-16 mags during my evaluation and did not need to modify the feed lips or follower for proper feeding. I managed to squeeze 11 of the fat cartridges into a 30-round mag and seven rounds into a 20-round mag. Manufacturer’s Note: A 30-shot magazine will hold 10 rounds, a 20-shot magazine will hold 6 or 7 rounds (dependent upon the follower) and a 10-shot magazine will hold 3 or 4 rounds of the .458 SOCOM. The rounds sit one atop another rather than in a staggered fashion as with the 5.56 rounds. I found it easy to load the cartridges even when the magazine was reaching its top capacity. Just like with the 5.56mm round the magazine will lock the weapon’s bolt back after the last shot.
The LAR-458 comes standard with RRA’s excellent two-stage target trigger. My sample broke at exactly 4 pounds with virtually no overtravel. This trigger is non-adjustable and if the gun is going to be used for tactical work I think this is preferable. There are no adjustment screws that might back out during firing and tie up the weapon. My carbine’s crisp trigger made it possible to shoot the weapon accurately.
My choice of optics also aided in my ability to produce small groups with the LAR-458. Given its softball-like trajectory, I think the .458 SOCOM will shine at ranges less than 150 yards. Therefore I decided to use a Trijicon Compact ACOG (Advanced Combat Optical Gunsight) for my accuracy evaluation. The scope is a compact design based on the tremendously successful ACOG that has found a very popular following with our troops in harm’s way.
My test sample features 1.5x and also possesses dual illumination: In sunlight the fiber optic daylight collector illuminates the aiming point and tritium powers the aiming point when there is little or no ambient light. Its extended eye relief is especially appreciated given the recoil of the weapon.
Halfway to the range I cursed myself. I had forgotten my PAST Recoil Shield, which I pack anytime I have to benchrest a gun with significant recoil. Rather than turn around and go home I continued on – after all, how bad could the recoil be?
If you’ve done a lot of AR shooting then you’ve probably accumulated the associated muscle memory and that is what makes shooting the Rock River Arms LAR-458 CAR A4 .458 SOCOM so deceptive. Everything feels exactly the same as a 5.56mm weapon so when I added the 4 pounds of pressure necessary to break the LAR-458’s trigger, it was like getting hit with a pillowcase full of nickels.
The sharp toe of the buttplate felt like it was digging deeper with each successive shot. I took a towel that I had brought along to wipe the sweat from my brow and folded it over and put it between my shoulder and the rifle’s butt. That provided enough relief and allowed me to finish my bench testing of the LAR-458.
In all, I fired 70 rounds from the bench that day and that was about all I could handle. If you’ve fired a .308 from an ultra lightweight bolt gun or spent a session with a pump gun shooting slugs you’ll have an idea of what it’s like to shoot the .458.
Shooting the rifle offhand is entirely different, though. The shooter’s body acts like a shock absorber and is freer to move than when shooting from a bench. I was actually able to make some respectable double taps on a target set up at about 20 yards. Rounds impacted about 4 inches apart.
I only had two different loads, both from CorBon, to test the LAR-458 with. One was a 300-grain jacketed hollow point and the other was a 405-grain jacketed solid point. Both rounds produced plenty of practical accuracy. Groups were fired at 50 yards, five shots to a group. I am certain that the LAR-458 possesses more accuracy than I was able to wring from it.
Throughout the testing the LAR-458 fed, chambered, fired, extracted and ejected every round that I put into it. There were no stoppages or mechanical problems of any sort. I’ll save you the details about field-stripping the LAR-458, as it is exactly the same as any standard AR-15. One recommendation that I can make is that if you buy a .458 SOCOM buy a .50 cleaning brush. I attempted to use a brush that I normally use to clean .45ACP barrels and it skidded through the barrel barely making contact.
The power the .458 SOCOM provides in the lightweight portable carbine is impressive. It will provide the department or agency with another tool, whether it is to defeat an engine block or a target behind hard cover, without the burden of extra weight or size. The LAR-458 will be especially useful in areas where wildlife and/or livestock sometimes intersect with vehicles.
The LAR-458 functioned perfectly and possesses excellent practical accuracy. Rock River Arms has legitimized the cartridge by building a production gun that needs no modifications or tuning to work 100 percent. Whether you’re a hunter, police officer or a savvy, defense-minded individual the .458 SOCOM will give you the power and penetration you crave without going to a larger weapon.
It was the Special Forces need for more power and penetration that became the inspiration…
by Jenny Gurvich / Dec 28, 2008