Knight's Armament SR-15E3 IWS Mod 1

posted on March 21, 2015

After being involved in the firearm industry for many years, C. Reed Knight Jr. of Knight's Armament was joined by renowned arms designer, Eugene Stoner, in 1990. Stoner worked there until his death in 1997. In 1991, Stoner designed the 7.62 NATO SR-25 rifle (Stoner Rifle-25), an upgraded variation of his original AR-10. The SR-25 was adopted by the U.S. Navy SEALs, and later evolved into the M110 Sniper Rifle used by the Army and the Marine Corps.

Following the success of the SR-25, Knight's Armament turned to the AR-15 platform, and designed the Stoner Rifle-15 (SR-15), a rifle with a number of advanced design improvements. The latest version is the SR-15E3 IWS Mod 1 (Integrated Weapon System, Modification 1).

The SR-15E3 IWS Mod 1 comes with a 16-inch, chrome-lined barrel with a 1/2x28 threaded muzzle and an A2 flash hider. At 3.75 inches from the front of the flash hider, a mil spec Upper Receiver Extending (URX) 3.1 Rail System begins and mounted atop is Knight's folding front sight. At 2.5 inches from the front of the rail are integral 3- and 9-o'clock side rails also measuring 2.5 inches, and both of these contain QD sling mounts at the front and a hex-head bolt at the rear. On the front of the bottom section of the handguard is a 2-inch rail and QD sling mount, and about 4 3⁄8 inches from the SR-15E3's muzzle is a low-profile, mid-length gas block housed beneath the top rail.

At the rear of the three short rail sections, the side and bottom sections of the handguard narrow approximately .105 inch to reduce the width of the fore-end by about .25 inch to 1.95 inches. The entire 7 5⁄8-inch length of this reduced width consists of a smooth surface. Five interspersed holes are present, with those of the side sections leading to threaded holes in the sides of the bottom rail where it interlocks with tracks within the main top rail. At the rear of the smooth sections are three more short rail sections. Those at 3- and 9-o'clock have QD sling mounts and hex bolts like their front counterparts.

Along with two QD sling swivels, four proprietary Knight's rail panels are furnished with hex bolts and nuts to affix them along the side and bottom rail panels. While mounting the panels is slightly tedious, once in place they will likely never be moved. The same is true of the bottom rail with its heat shield. Inside the rear of the railed fore-end is a proprietary barrel nut that locks it rigidly and perfectly in line with the upper flattop receiver tail using a precise fixture during mounting. This renders the two-piece rail as rigid as a monolithic system, still while allowing a damaged fore-end to be replaced.

Made from mil-std aircraft-alloy forgings, the flattop upper receiver mates perfectly with the lower receiver and both display a high-quality exterior. Surpassing mil spec, the upper receiver comes with ambidextrous charging handle locks, suggesting such a handle exists or is planned. The charging handle has Knight's well-designed extended latch. Also standard is its adjustable flip-up, peep-aperture rear sight.

Furnished for evaluation was a set of Knight's excellent new 45 Offset Flip Sights, for use when a high-power optic is mounted.

Deserving special mention is the SR-15's bolt, from which the rifle gets its E3 designation. Where the standard AR-15 bolt uses seven rectangular-shaped locking lugs, Knight's bolt has lugs that are rounded both on the top and bottom. The same design is used in the corresponding lugs of the barrel extension. Radii eliminate stress risers, and the extra material provided reportedly increases the lug strength by at least 50 percent. Sharing the spotlight is the cam pin, which (with the firing pin) is of a smaller diameter. This allows the bolt walls to be thicker.

Equally advanced is the SR-15E3 IWS Mod 1's dual-spring extractor.  Extractor problems in the AR-15 are often due to centrifugal force, as the bolt rotates to unlock. The "E3" extractor is wider at the rear to house two springs, and the extra material adds weight to help balance the extractor's front portion from backing away from the cartridge-case rim as it rotates.

The SR-15E3 IWS Mod 1's lower receiver includes Knight's ambidextrous magazine release, bolt release and safety/selector, and comes with a proprietary, enlarged fold-down trigger guard. Ambidextrous single-point QD sling mounts are located on the rear sides of the receiver. Also standard are extended M4 feed ramps and Knight's 2-stage Match Trigger. For the buttstock, Knight's has chosen the SOCOM buttstock produced for the military by Lewis Machine & Tool. Made of tough polymer, this stock has two waterproof full-length battery compartments, two ambidextrous sling mounts and a nonslip rubber buttpad.

Operations of the sample SR-15E3 IWS Mod 1 were exceptionally fine. Unlike some ARs, the SR-15E3's charging handle was quite smooth. The magazine release proved equally smooth, and the Knight trigger is suitable for any type of shooting. With a crisp let-off of 4.5 pounds, this trigger proved excellent in all respects, and the ambidextrous safety has the lower half of the thumb pad machined flat to stay out of the way of the index finger.

The SR-15E3 IWS Mod 1 was tested using its open sights informally from the shoulder with a variety of 5.56 NATO ammunition and from sandbags using a Leupold 3-9x40 mm MR/T scope. The rifle preferred some bullets and brands to others, but generally produced excellent accuracy hovering near 1 MOA. There were no malfunctions during the tests.

Because of its exceptional quality, Knight's Armament's new SR-15E3 IWS Mod 1 would seem an ideal carbine whether for home defense, hunting or law enforcement.

Manufacturer: Knight's Armament; (321) 607-9900,
Action Type: Direct-gas-impingement, semi-automatic
Caliber: 5.56 NATO
Capacity: 30 rounds
Upper Receiver: T7075 mil spec aluminum
Barrel: 16 inches, cold-hammer forged, chrome lined
Rifling: 6 grooves; 1:7-inch RH twist
Fore-End: Knight's Armament URX
Lower Receiver: T7075 mil spec aluminum
Trigger: Two stage, 4.5-pound pull weight
Sights: Steel; flip-up adjustable for elevation (front), flip-up peep aperture adjustable for windage and elevation (rear)
Stock: Lewis Machine & Tool SOCOM
Length: 33 to 36.25 inches
Weight: 6.6 pounds
MSRP: $2,207.50

Shooting Results

Load Velocity   Group Size  
    Smallest Largest Average
Black Hills 52-grain Match JHP 2,998 1.08 1.24 1.17
Federal 55-grain FMJ 2,961 .87 1.05 0.97
Remington 55-grain MC 2,952 1.41 1.64 1.52
Winchester 50-grain BST 3,021 1.17 1.28 1.22

Velocity measured in fps 15 feet from the muzzle for 10 consecutive shots using a Pro Chrony LE 15 chronograph. Temperature: 82 degrees Fahrenheit. Accuracy measured in inches for five consecutive, five-shot groups at 100 yards from a benchrest.


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