The KS series of rifles are developed and manufactured by Knight’s Armament Company (KAC) as modernized successors to their AR-based SR-16 models. The 13.7-inch KS-1 variant was officially adopted by the British Armed Forces in 2023, receiving the designation L403A1-AIW (Alternative Individual Weapon). It is intended to complement and gradually replace the L85A2-A3 and L119A1-A2 rifles currently in use by the Royal Marines and the British Army Ranger Regiment.
Development and Service History
First introduced at military small arms expos in 2022, the KS rifle family was created to meet an international special operations forces (SOF) requirement. In September 2023, the UK Ministry of Defence selected the KS-1 under Project Hunter to serve within elite British Army Special Operations Brigade units and Royal Marines strike companies, including their Surveillance and Reconnaissance Squadron.
The British military’s order includes over 1,600 rifles valued at approximately £15 million, with the Royal Marines acquiring more than a thousand units. Knight’s Armament’s KS-1 was chosen over competitive entries from companies such as Heckler & Koch, SIG Sauer, Daniel Defense, and Glock. Furthermore, the UK MoD holds an option for purchasing up to 10,000 rifles over the next decade, with a contract ceiling of £90 million.
Design Features
The KS rifles employ a highly efficient gas system with a straight gas tube and a self-indexing design that reduces gas pressure loss between the gas block and bolt carrier. The gas block is secured via a nut, facilitating quick removal and maintenance.
The weapon’s bolt carrier group incorporates Knight’s Armament’s proprietary E3.2 Enhanced Bolt, featuring an enlarged bolt face, dual ejectors, rounded bolt lugs, a reduced diameter cam pin, and uniquely designed extractor and firing pin components, all contributing to increased durability and reliability.
A standout feature is the fully ambidextrous lower receiver, with mirrored controls for safety, magazine release, and bolt catch/release on both sides. This ambidexterity places the KS series among the few military fielded M16/M4-style rifles offering complete dual-sided operation.
Additional components include Knight’s Quick Detach Coupling (QDC) flash hiders and a drop-in two-stage match trigger. The barrels are cold hammer forged and chrome-lined for enhanced longevity. The rifles also feature the URX 6 free-floating handguard, covering the barrel length to provide protection and improve accuracy. Chambered in 5.56×45mm NATO, the KS series is offered with barrel lengths of 11.5″, 13.7″, 14.5″, and 16″.
Variants
- KS-1: 13.7-inch heavy-profile barrel with a mid-length gas system, featuring ball-mill dimpling for weight reduction and thermal stability. When combined with a compact high-efficiency suppressor, it matches the length of a suppressed 10.3-inch M4 carbine but offers greater muzzle velocity.
- L403A1: The British military’s designation for the KS-1, fitted with the L900A1 Optics Suite—comprising a Vortex 1–10x low-power variable optic and Aimpoint ACRO P-2 red dot sight—paired with KAC’s QDC/MCQ-PRT 3D printed Inconel suppressor that reduces backpressure.
- KS-2: Features a 14.5-inch barrel and mid-length gas system.
- KS-3: Equipped with an 11.5-inch barrel and carbine-length gas system, offering compactness for ease of transport and handling. Its compatibility with other KS rifles makes it an ideal secondary upper receiver or a primary weapon for those needing a lighter carbine.
- KS-4: Sporting a 16-inch barrel with an extended mid-length gas system, utilizing a longer URX handguard variant.
Users
- South Korea: The KS-3 is in service with the Korea Coast Guard and the 707th Special Mission Group.
- United Kingdom: Designated as the L403A1, the KS-1 is operational with the Royal Marines and British Army Ranger Regiment, replacing the SA80 rifle family.
