The Knight's Armament Corporation (KAC) SR-15 Individual Weapon System (IWS) features a number of subtle and important improvements over standard AR-15/M-16 style weapons that many users are not aware of. These improvements may not be noticable at first glance, or at all to the average user, but those in the know are always impressed by KAC's attention to detail. Let me give you a guided tour!
When the SR-15 E3 was designed, KAC paid particular attention to look at the system as a whole. KAC relooked the entire weapon system's operation to identify weaknesses to be addressed, as well as strengths that could be further improved.
![Knight's Armament Corp SR-15E3 upper]()
Durability and Reliablity
AR-15/M-16 bolts all break eventually, especially under harsh military firing scheduled. US SOCOM's special operations soldiers are advised to replaced their bolts every 5,000 rounds, given their specialized and harsh firing schedules. SOCOM has been very interested in integrated electronic round counters to go from a reactive maintenance program, to a pro-active one, as AR15/M16 bolt failure is inevitable, and unpredictable.
The SR-15 E3 addressed the durability concerns of standard AR-15/M-16 rifles in a number of ways. The first, and most important upgrade is the proprietary E3 bolt used on SR-15 rifles. These bolts feature thicker bolt lugs with nearly 50% more material. The beefed up and rounded lugs increase service life significantly.
![SR-15 E3 vs. AR-15 Bolt]()
The proprietary E3 bolt requires a proprietary barrel extension, meaning that this upgrade is not backwards compatible. Only KAC SR-15 rifles can utilize the E3 bolt system.
![E3 barrel extension]()
The SR-15 bolt also uses two extractor springs (twice as many as standard bolts), a deep extractor channel, and optimized geometry to ensure extraction reliability under harsh conditions. The extractor pin has also been beefed up, and is not held in place by a spring on the extractor instead of just tension.
![The SR-15 bolt features an improved extractor design]()
Lastly, the SR-15 firing pin is designed to be lighter to provide faster ignition, lowered chance of slam fire, and reduces the size of the cam pin's cavity and most obvious structural weakness.
![SR-15 vs. AR-15 firing pin and cam pin.]()
Controllability
The SR-15 is one of the lightest tactical rifles on the market, and because of Netownian phsyics (mass and force etc) one would assume felt recoil would be greater on SR-15 rifles. As it turns out, the SR-15 manages to have its cake and it eat it too, as the barrel features two subtle improvements which are responsible for the SR-15's light recoil.
SR-15 rifles use a proprietary gas system length, along with a tuned gas port size to optimized the amount of gas delivered to the operating system. With an optimized amount of gas, there is no excess stress placed on operating components as is common with rack grade rifles that are usually "over gassed".
The barrel itself is cold hammer forged, and on a lightweight profile, meaning that with a good butt stock pairing (Complete SR-15s use LMT SOPMOD stocks), the rifle is not at all front heavy, and very balanced and easy to point and control.
Practical Ergonomics
The SR-15 was engineered as a complete weapon system, and as such, it features some of the best ergonomics every utilized on a rifle. Unrestrained by bureacracy or institutional inertia. KAC made a number of significant improvement to the practical ergonomics of the rifle.
Long before it became a popular trend, the SR-15 featured a cold hammer forged, lightweight profile barrel which makes the rifle superbly durable, pointable, and accurate.
There are a number of small, but nice touches on the rifle. There are 4 QD sling swivel socket locations on the URX-II rail, affording users a lot of options.
![4 QD sockets total]()
The integrated sight features a match grade "skinny" front sight post, and is easily adjustable by hand with not tools.
![SR-15 Integrated Front Sight]()
The rear sight is match grade, and allows users to easily dial in for engagement up to 600 yards
![_DSC0777]()
In conclusion, the SR-15 upper receiver has a lot of improvements and upgrades. While you can find similar upgrades from other companies, finding all these upgrades on one cohesive, professional designed and assembled package, all for $1299, is quite a treat.
This is a premium AR-15 style upper receiver, but there is just ONE weakness in the current configuration in my opinion. The exposed gas block utilizes two set screws, and while i've never seen a SR-15 gas block come loose in the many SR-15 rifles and uppers i've sold, I would prefer if this gas glock was pinned in place. Luckily, Weapon Outfitter's gun smith offers this service for $30 for users who need absolute peace of mind.