HK, Bushmaster, and Rock River: Semiauto Field Rifles In Heavy Trim

We tested a trio of .223s - the HK SL8-1, a Bushmaster Varminter, and a Rock River Varmint - to see which gun offered the best combination of accuracy, features, and shootability.


Most shooters who envision a varmint rifle see a big, heavy bolt gun perched atop a shooting bench, with prairie dogs 300, 400, and 500 yards or more distant. The shooter carefully loads a single .22-250, 6mm PPC, or other handloaded round and chambers it. After gauging the nearby wind with smoke from a fine cigar, the shooter lays down on the stock and fires. The light recoil from the gun scarcely moves the rifle or shooter.

That may be the mental image you have of varmint rifles, but at least two AR-15-style manufacturers, Rock River and Bushmaster, are making the “black gun” in heavy-barrel configurations and marketing the .223 Remingtons as appropriate for accuracy shooting. In that same vein, another manufacturer, Heckler & Koch, is marketing a variant of its G36 assault rifle as a heavy-barrel accuracy rifle for the U.S. market.

What struck us as unusual in this matchup was the marrying of a heavy barrel or other heavy componentry to what was originally a lightweight field rifle configuration. Though there are plenty of differences between the guns in terms of features and designs, one thing we would expect from all three is that they should shoot accurately. So we acquired a grey polymer-stocked HK SL8-1, $1,249; a Bushmaster Varminter, $1,200; and a Rock River Varmint, $950, to see which gun offered the best combination of accuracy, features, and shootability. We were also very curious to see how the oddly shaped SL8-1 would fare against what has become the traditional profile of the AR-15 guns. (AR-15 is a Colt trademark, but we use that name here as a generic description of the category).

Range Testing
Our ammo selections included a range of bullet styles and weights, mainly to see which barrel twist rate would stabilize which bullet the best. Varmint hunting, the use for which the two AR-15s were purportedly built, ranges from long-distance prairie dog shooting to short-range coyote hunting. Bullets for these divergent uses can range all over the .223 weight spectrum. However, the SL8-1 doesn’t carry a “varmint” description, and HK’s literature doesn’t cite a specific use for its rifle. So we tended toward the upper end of the .223 weights to ensure we got a mixture of bullets that would likely serve in many conditions.


For the accuracy section, we shot five five-shot groups of the PMC 223B 55-grain Pointed Soft Points, Winchester USA full-metal-jacket 62-grain rounds, and 69-grain boattail hollowpoints from Federal, the Gold Medal Sierra MatchKing loading. We fired the guns on a hot, muggy, overcast day that, thankfully, had light 6 o’clock tailwinds, which made reading the wind easy and swept away mirage. We used a Ransom rifle rest on the front and stabilized the buttstocks on the two AR-style guns with a Protecktor bunny bag. The HK buttstock was too deep for the Protecktor bunny bag, so we used a pair of sandbags to keep the buttstock from wiggling. For the chronograph data, we used an Oehler 35P unit attached to a printer. We scoped the guns with a IOR Valdada 2.5-10X42mm riflescope carrying Weaver-style clamp-on rings.

We noticed some speed oddities. The HK gun showed lower velocity readings across the board, as much as 278 fps between it and the Bushmaster Varminter shooting the Federal Sierra Matchking 69-grain hollowpoints.

On the accuracy side, however, we were pleased with how all the guns shot. The largest average groups in the test came with the inexpensive Winchester USA 62-grain rounds. Neither the 1-in-9 twist Bushmaster nor the 1-in-7-twist HK liked that round much, shooting 1.5- and 1.6-inch groups with it respectively. But the round didn’t bother the 1-in-8 twist RR Varmint, which shot the Winchesters into 0.9-inch groups. All the guns shot the 55-grain PMC fodder within tenths of an inch of each other. The Bushmaster and HK guns did slightly better with 1.1-inch average groups apiece, followed by the 1.2-inch readings for the RR gun. The RR and HK guns shot the best average groups of the test using the 69-grain Federal Sierra MatchKings, posting 0.8-inch averages. The Bushmaster was back a step at 1.3 inches.

Overall, we would have to give the edge in accuracy to the Rock River gun. Its largest group was only 1.2 inches, and it shot two rounds under an inch. The HK came in second, we feel, on the strength of its 0.8-inch showing with the MatchKings, followed by the Bushmaster’s best group at 1.1 inches.

Here’s what we thought of the guns individually:

HK SL8-1, $1,249
During NATO’s ground deployment in Kosovo, the year of 1999 marked the first time since World War II that German soldiers were in combat, and they were using the newly developed Heckler & Koch G36 5.56mm rifle. The G36 is a modular weapon system in caliber 5.56x45mm NATO. The barrel of the G36 can be exchanged by unit armorers to create a Rifle, Carbine, or a light support Variant using the same common receiver. Tested and currently fielded with special units of the German Armed Forces (including the new NATO Rapid Reaction Force), the G36 is now available to U.S. law enforcement.


The HK SL8-1 .223 was introduced into the commercial market in 1999. The SL8-1 is a child of HK’s G36 assault rifle, though they are cosmetically very different. Unlike earlier HKs, the G36 uses a gas system similar to the Armalite AR-18. The G36 makes heavy use of synthetic materials, including the receiver. The bolt assembly and barrel account for most of the metal in the G36 rifle, making it, and its civilian counterpart the SL8-1, lightweight and very corrosion resistant.

The HK SL8-1, which we’ve seen selling for a dealer price of $1,200 from SOG, (800) 944-4867, is mostly constructed of a carbon-fiber reinforced polymer. It uses a short-stroke, piston-actuated gas operating system with a rotary locking bolt. It houses a Stoner-style rotating bolt, cam piece, firing pin and firing pin retaining pin. The chrome-plated bolt is machined with six locking lugs.

The gun, chambered only for .223 Remington, employs a single-stack polymer magazine that accepts 10 rounds. The barrel rifling is a right-hand 1-in-7 twist. The barrel is hard-chrome plated and cold-forged with the chamber.

Overall, the gun measured 38.6 inches in length and was 2.4 inches thick. The barrel was 20.8 inches long, with a sight radius of 19.7 inches. It was 9.8 inches tall. The gun we tested weighed 8.6 pounds with an empty magazine.

The SL8-1 diverges from the G36 in a number of ways, of course, starting with the thumbhole stock. It’s a light gray color with a contrasting black adjustable cheekpiece and buttstock. The stock lines are very unusual, with an angular, cut-forward forend showing only 6.75 inches of barrel. The grip drops to a point 3 inches below the trigger guard, and the blocky buttstock is adjustable for LOP. An adjustment tool—HK’s rifle equivalent of a Swiss Army knife—is included.

The barrel on the SL8-1 is a heavy contour 1-in-7-twist tube, tapering from 0.84 inches at the chamber to 0.79 inches at the muzzle. The 1-in-7 twist ratio implies that heavier bullets such as Sierra’s 69-grain HPBT would shoot best in the gun, which is what we found. The barrel extension is molded into the receiver, and the barrel is secured to it with a cylindrical nut that is slotted at 90-degree angles. Also, the barrel is free-floated away from the polymer forend.

The SL8-1’s single-stack translucent plastic magazine is unique to the gun. It accepts up to 10 rounds of .223 Rem. (5.56mm NATO) ammunition. The magazine is a little hard to load until the shooter learns to push the round down and back properly. To our knowledge, no high-cap magazines are available for the SL8-1, and G36 magazines will not work. Reason: HK was forced to modify the G36’s existing magazine system for sale in the U.S. so that the SL8 couldn’t accept its forebear’s magazines. SL8s sold outside this country employ a 10-round, staggered, cropped G36 magazine.

The magazine release is a wide, flat tab located in front of the trigger guard. Pushing it forward allows the magazine to drop out, and its location allowed us to make single-handed magazine changes. When the last shot in a magazine is fired or when the SL8’s cocking handle is pulled back with an empty magazine in place, the follower engages a bolt catch integral with the fire-control housing. Without a magazine in the gun, the shooter can also hold the action open by retracting the cocking handle and pressing a button in front and above the trigger. The bolt can then be released by lightly pulling back the cocking handle and allowing it to push forward. In our view, getting to the ambidextrous cocking handle was blocked in part by the low sight rail.

The standard sight rail extends across the topmost length of the gun, and the polymer rail will accept virtually any type of optics. However, it’s contradictory, we think, that the gun ships with the standard open sights. The fixed front blade is too coarse for precision use, in our view, but it is shielded. The rear sight, an unshielded L-type, allows the shooter to flip between 100 and 300 meter aperatures. To make adjustments, the owner must turn 2mm allen-head screws (wrench provided), but to our eyes, the process isn’t easy. Still, the sight rail readily accepts optics like the scope we used, and there were enough crosscut slots to get acceptable eye relief.

Shooting the gun, we found the unconventionally designed stock to be both easy and not easy to handle. The forend is squarish, but the corners are beleved off. This allows the gun to sit comfortably in the hand, especially in the area just in front of the magazine well, or on the bench without rolling. To attach a sling, the shooter can fasten a swivel or hook into a hole in the molded stock.

Unlike the two ARs tested elsewhere, the HK’s rear stock is adjustable. The buttplate slides in and out of the hollow stock. Two allen head screws lock the stock down. There is 1.6 inches of length adjustment, which is made with the tool set’s 5mm allen wrench. (HK sells extra stock spacers for $6.) A hard-rubber buttpad and a polymer sling attachment are molded into this sliding assembly. The cheekpiece, mounted to two flush-fitting, threaded steel inserts, allowed us to get exactly the cheek pressure we wanted. The cheekpiece and one spacer are supplied with the rifle. Extra spacers are available.

Though we liked the variability of the butt and cheek portions of the stock, the thumbhole offers a weird handfit. Built to accommodate lefties and righties, the big hole in the stock is cut so far forward that even people with short fingers tended to overrun the trigger, forcing the first joint rather than the finger pad to make the gun fire. Also, the front portion of the thumbhole needed to be relieved and thinned on the opposite side of the stock, we think. We weren’t able to find a completely comfortable way to hold the trigger-finger hand on the gun; but we recognize there’s a variety of hand sizes and builds which would contradict our experience. The ambidextrous cocking lever was a nice addition so that right- and left-handed shooters could operate the gun.

Some observers have complained about the SL8-1 being very front heavy—and it would seem this point could be easily resolved yea or nay. We found the balance point to be right in front of the mag well, and shooting the gun standing, with the elbow on the rib cage, was very comfortable. However, because of the thumbhole grip, we liked to cant the gun heavily toward the face. In kneeling and prone, the forend fit the front hand well.

We found the trigger was better than we expected, though it didn’t have the qualities we normally like. We prefer two-stage triggers on most rifles, where between half and three-quarters of the total trigger take-up weight is pulled up in a clean, smooth stage. That leaves a minimal amount of force needed to break the trigger in the second stage. The SL8’s trigger broke at 5 pounds, which isn’t as bad as many rifles we’ve seen. But the front end of the pull was soft, leading to an indistinct “area” of break, rather than a point of break. However, we found that pulling up the slack, then firmly pulling through the release point, gave us good control.

As we’ve noted, the gun ships with tools, including 2mm, 2.5mm, 3mm, 4mm, 5mm, and 8mm hex wrenches as well as phillips and flathead scewdrivers. The 2mm hex wrench adjusts the fixed sights. The 2.5mm hex wrench adjusts carry handle optics. The 5mm hex wrench adjusts or removes the stock. The phillips head screwdriver removes the sights, sight rail or carry handle. We appreciate them providing it as a package rather than charging extra for it.

After finishing our range work, we broke the gun down to see about cleaning it. We saw that the bolt and chamber area of the rifle showed little signs of fouling. In our view, the gas system does not allow many contaminants into the action, eliminating much of the fouling common to the M16/AR-15 clones.

Accessories include the SL8-1 Buttstock Spacer, $6; SL8-1 Cheek Piece Spacer, $7; G36C/SL8-1 Picatinny Rail Short, Polymer, $30; G36/SL8-1 Front & Rear Tritium Sight Set (green front dot with two-dot green rear sight), $170; Eye Bolt, Sling/Bipod, for G36 Forearm or Knight’s RAS System, $20; and many others.

Bushmaster LR-24V Varminter, $1,200
Bushmaster Firearms, Inc. of Windham, Maine, originally a supplier and manufacturer of AR-15 parts, is now one of the largest producers of AR-15/type rifles for civilians. The Varminter is a variation on the Bushmaster AR-15 platform.


It carries a 24-inch fluted 4150 chrome-moly steel barrel, which measures 1 inch inside the aluminum handguard down to 0.75 inch forward of the gas block. The competition-crowned barrel has a 1-in-9 twist. The gun comes with the Bushmaster competition trigger, with what the company claims is a smooth, two-stage, 4.5-pound pull. The V Match tubular forend free-floats the barrel from the action. The forend has cooling vents for increased barrel heat dissipation. Underneath the handguard is a bipod stud, a nice feature on a varmint gun. A Hogue rubber shell covers the pistol grip portion of the frame. The grip surface is textured, ambidextrous, and grooved for correct trigger-finger placement.

Other features include 1/2-inch-tall Mini-Risers, slight blocks that elevate a scope above the flat-top receiver so that the optics clear the charging handle, controlled ejection path so that shells drop nearby, and a lockable hard case. The gun comes with a single five-round magazine. But the rifle will accept any AR-15 type magazine, such as those pre-bans you have stashed with your socks.

It measures 42.25 inches in overall length. The barrel has a right-hand 1-in-9 twist with six grooves/lands. It weighs a hefty 9 pounds with an unloaded magazine.

Compared to other Bushmaster products, this is a pure shooting machine. It lacks a muzzle brake, flash hider, bayonet lug, flashlight, laser sight, or other geegaws. The flattop design cries out for a scope, and the two Weaver-type riser blocks are a big help in mounting optics where they won’t hamper the gun’s function.

The round, mostly checkered handguard is made of vented aluminum and allows the barrel to float free of sling stress. The handguard is also fitted with a bipod or sling-swivel stud mount. Though the Bushmaster’s handguard fits great in the hand, it rolls pretty badly on a bench rest. We think it would have shot under an inch with at least one ammo had we been able to control the gun a little better.

Break-in on the barrel was lengthy. For the first 60 rounds, Bushmaster recommends firing no more than 20 rounds at one time before cleaning the barrel. The company also recommends a specific cleaning procedure, which includes pushing cleaning tools from the breech toward the muzzle and then removing them from the rod at the muzzle end. Bushmaster emphasizes that tools not be dragged back through the muzzle, probably to avoid damaging the crown. Also, the company recommends cleaning first with a good bore cleaner, followed by a copper solvent, followed by a regimen with JB Bore Cleaner paste. We followed this procedure as recommended, and amended it for use with the other guns.

The barrel profile isn’t as thick as the Rock River gun’s, and it’s on par with the HK. The barrel measures 1 inch in diameter inside the handguard and 0.745 inch forward of the gas block. Of the three guns, the Bushmaster was the easiest to point when taken off the bench, though we still wouldn’t want to carry it too far to shoot.

The two-stage competition trigger had a 3.5-pound first stage and a 1-pound second stage, or 4.5 pounds overall. That’s a good ratio of trigger-tension distribution, ensuring reliable function but a manageable release weight. The trigger was adjustable for weight of pull and overtravel. Our sample’s trigger was uneven during the first stage (which could easily wear in better with more use), and the second stage was damn near perfect—crisp, fast, sure.

We had no function problems, and we noted that the brass didn’t fly all over creation upon ejection. Feeding was smooth, and we had no occasion to use the forward assist.

The Bushmaster and RR guns didn’t offer the buttstock adjustability of the HK gun, which was a a decided advantage for the SL8-1, in our view. We liked the soft rubber Hogue pistol grip, which was deeply grooved and tacky. It enhanced the rifle’s handling qualities.

Rock River Varmint .223 Rem., $950
Rock River Arms is based in Cleveland, Illinois, and like Bushmaster, it supplies a variety of guns and gun parts. The Varmint is a new series of heavy-barrel AR-15s, with barrels ranging from 16 to 24 inches in length. They each sell for $950, irrespective of barrel length. We shot the 24-inch gun, which comes with a .223 Wylde chamber sizing and 1-in-8 and 1-in-12 twists. We shot the faster twist in this test. The Varmints come in two upper styles, a standard A4 flattop and the one we tested, the EOP. That stands for Elevated Optical Platform, and like the riser blocks on the Bushmaster, the EOP allowed easy use of a riflescope by raising the mounting plane an inch higher.


The gun’s Wilson air-gauged stainless-steel bull barrel measures 1.05 inches under the aluminum handguard and 0.92 inch forward of the gas block. The gun comes with what the company calls a National Match two-stage trigger. The tubular handguard has the barrel free-floating forward of the action. The handguard lacks cooling vents and checkering like that found on the Bushmaster. Underneath the handguard is a bipod/sling stud. The grip appears to be the same Hogue model as the Bushmaster’s. The gun comes with two five-round magazines, but will accept other AR-15 magazines. It measures 42.25 inches in overall length and weighs 10 pounds, the most in the test.

Compared to the other guns, this gun appears not to compromise accuracy for weight. It is noticeably heavier than the other guns, which for a gun labeled for “varmint” use isn’t such a big deal. But it is a load to carry, and we would not like to stay slung up on it in prone too long a time either. Shooting standing with the gun is tiring; moreso, we think, than the other two guns because there’s so much muzzle mass to deal with.

That said, the RR would shoot. It is unusual to find a factory gun that averages under an inch with just any old ammo we feed it, but the Varmint liked both the Federal and Winchester rounds, as we noted above. This was even more remarkable because the round handguard wasn’t all that firm on the benchrest and the trigger wasn’t as light as we would have liked at 8 pounds total weight. Only about 2 pounds of that total were in the first stage. That said, the let-off was crisp and consistent, so we always knew when the gun would go bang.

Unlike on the Bushmaster, there wasn’t any break-in needed. A reader-service card enclosed with the gun said the barrel came lapped from the factory, and break-in wasn’t necessary. So we took Rock River at its word and just shot the gun, which is guaranteed to deliver 0.75-inch accuracy at 100 yards. Our best group average approached that, and we did shoot several groups smaller than that with each test ammo.

Gun Tests Recommends
HK SL8-1, $1,249. Our Pick. This was a tough choice, because each of these guns had plenty to recommend it. Ultimately, the HK’s buttstock adaptability, weather-resistant design, and trapezoidal forend gave it an edge.

Bushmaster LR-24V Varminter, $1,200. Buy It. This gun shot near MOA, and we think it would do better than that with a little tuning. It had the best trigger of the group.

Rock River Varmint, $950. Buy It. Shot the best, cost the least by a sizable margin. With two small additions — a different handguard shape and a lighter trigger — we might have picked the Varmint over the HK. We also recognize that many shooters will prefer the domestic ARs over the HK any day, and in this test, we can’t say that’s a bad decision.






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