Knight's Armament Company SR-47

The SR-47 is a modern rifle based on the AR-15 family of rifles created by Knight's Armament Company for USSOCOM. Unlike the majority of ArmaLite-type guns, the SR-47 is essentially an AR-15 that fires the Soviet 7.62×39mm round from AK-47 magazines, which explains the "47" in the gun's name. The rifle was created after soldiers on long missions in Operation Enduring Freedom complained of running out of 5.56×45mm NATO ammunition for their M4 carbines but having plenty of captured AK-47 magazines. The SR-47 is basically an M4 that will accept standard AK-47 magazines rather than NATO STANAG M16/M4 mags, along with other minor modifications common to KAC's designs.

Development
The SR-47 is an outgrowth of the Colt M4 Carbine's SOPMOD system. After the September 11, 2001 attacks, SOCOM placed a proposal through DARPA for a system that would allow an M16 rifle or M4 carbine to fire 7.62x39mm ammo fed from common or standard-issue Kalashnikov magazines.

Originally it was going to be a series of drop-in parts (the Special Purpose Receiver - Variant, or SPR-V) to convert an M4 or M16 in the field to fire 7.62×39mm ammunition. This requirement was later expanded to require the weapon to accept and feed from standard Kalashnikov magazines. The complexity of this task made the planners rethink this approach. The idea of a complete weapon that could still use standard SOPMOD accessories (the Special Purpose Rifle - Variant) was born.

Three companies submitted samples: Lewis Machine & Tool (LMT), Robinson Armament (RAV-02), and KAC (SR-47). After a series of trials, the pack was narrowed down to the RAV-02 Robinson carbine and the KAC SR-47. The SR-47 was selected over the RAV-02 for two reasons. KAC was already a government contractor with a strong track record with a history of completing previous contracts. The KAC SR-47 had more parts commonality to the M16 / M4 weapons already in service and could use the same accessories.

Details
The SR-47 is based on the Knight Stoner Rifle (or SR) series. Many aspects of the rifle resemble an M16, but almost all parts are upsized slightly to handle the larger 7.62×39mm cartridge. The rifle uses a custom free-floating barrel manufactured by Obermeyer Barrel Co. of Wisconsin. It is machined to accept a custom Knight manufactured suppressor to reduce muzzle flash and moderate noise.

The magazine well is modified to accept standard AK box magazines. Although the standard AK magazines use steel or reinforced polymer, the standard KAC SR-47 magazines were made from aluminum alloy like the M16. The magazine well has an ejector spring to eject spent magazines and speed reload times.

Testing
Only seven rifles are known to exist. Six went to USSOCOM and one was retained in the Knight Co. museum. After field trials the weapon was not selected for service. The concept was dropped and a proposed variant chambered for 5.45x39mm M74 (to be dubbed the SR-74) did not enter into development.

Reasons for not adopting the weapon were not given. However, there might have been problems with the major flaws in the concept. First is that the Stoner gas system requires ammo that uses a non-corrosive propellant while the Kalashnikov system usually uses ammo that uses a corrosive propellant. This will cause rust and damage to the gas system if not cleaned regularly. Second is that the operators must rely on ammunition and magazines scavanged from the battlefield or taken from captured or killed hostile personnel. Magazines might be damaged, worn, or poorly maintained and cause stoppages when used. Ammunition might be old or corroded and might fail or be inaccurate. Third is that the weapon would need to use accessories keyed to the "new" 7.62x39mm M43 round, which would eliminate the advantage of the common 5.56x45mm-based SOPMOD system. Finally the 7.62x39mm round has a curved rather than straight trajectory and varying "zero points" depending on manufacturer and ammunition quality, making aimed shots difficult.

Usage
The rifle was reportedly in use by the bodyguard detachment of Afghan President Hamid Karzai. Furthermore, it's use has been acknowledged by the Bulgarian elite counter-terrorism forces the SOBT (СОБТ, in Bulgarian).

Related Projects
The Special Purpose Rifle was a parallel development. Originally it was going to convert the M16 rifle and M4 carbine to use an experimental cartridge that would be more accurate and hard-hitting at close and medium ranges than the standard 5.56x45mm NATO. The concept led to the development of the 6.5x39mm Grendel and 6.8x43mm SPC cartridges. The final development used improved and specialized 5.56mm NATO ammunition instead.

Colt had already developed two civilian semi-automatic AR-15 carbines chambered for 7.62x39mm. They were the R6821 Sporter Carbine with 2-position retractable stock and the R6830 Sporter Lightweight with fixed M16A2-style stock. They used unique parts and only fed from proprietary 5-round M16-style aluminum-alloy magazines, which discouraged widespread interest in the weapon.

In 2012 Rock River Arms began marketing a civilian rifle very similar to the SR-47 called the LAR-47. There are various carbine models with 16-inch barrels that come with 30-round box magazines. The LAR-47 X-1 target rifle model comes in two variants (one with a fixed stock and the other with a retractable stock) with 18-inch free-floating barrels and come with 10-round box magazines.

In June of 2014 Colt Defense unveiled the CK901, based on Colt's modular CM-901 system. It is a direct-impingement AR-AK hybrid that is similar to the SR-47. The standard carbine has a 16 inch barrel, a monolithic picatinny rail along the upper receiver, and a three-position accessory rail forend (sides and bottom). The carbine weighs in at 3.6 kg (7.9 lbs) without accessories and 4.5 kg (9.92 lbs.) with accessories (like the magazine, sling, and cleaning kit). A Short-Barreled Rifle (SBR) version with a 13-inch barrel is also rumored to be in the works. It comes with polymer 30-round magazines manufactured by US-Palm, but it can also feed from any AK-47 interface magazines.

US SOCOM have attempted to create a silenced close-range sniper weapon to rival the Russian VSS Vintorez and a Close Quarter Battle weapon similar to the Russian AS Val and SR-3 Vikhr. M4 Carbines have been converted to fire .300 AAC Blackout rounds. The .300 Blackout uses the same boltface as the 5.56mm NATO cartridge, meaning that only the barrel needs replacing. It can also fit in the same standard magazines as the 5.56mm NATO, as it is a straight-walled cartridge.