The KAC SR-47 is an SR-15-based assault rifle based on the AR-15 family of rifles. It was created by Knight's Armament Company for USSOCOM, but was never actually fielded. It is chambered in 7.62×39mm and accepts AK platform magazines.
The SR-47 entered and won the Special Purpose Receiver - Variant (SPR-V) program for the United States Army. The program searched for a drop-in set of parts that could be used on M16/M4 platform rifles for them to accept 7.62×39mm Kalashnikov magazines captured from insurgent forces. During the development of the SR-47, it became apparent that its design was too big to be a separate set of parts, so the SPR-V program changed its requirements to a dedicated weapons system instead of an individual receiver. This change in its requirements brought the new name: Special Purpose Rifle - Variant.
The rifle still, however retained some flaws. This wasn't because of the design of the rifle, but rather because of the idea behind the program. Ammunition and magazines captured from enemies would likely have been too old, damaged, or worn to actually use reliably in combat. Only seven prototypes of the SR-47 were made - six entered field testing, and the remaining one sits on display in the Knight's Armament museum.
The SR-47 is basically an SR-15 that will accept standard 7.62 AK magazines. All parts that are modified from the AR-15 on a standard SR-15 are modified on this rifle as well, with further modifications to accept the standard AK magazine. This rifle sports a custom barrel manufactured by Obermeyer Barrel Co., and is threaded to accept a KAC suppressor.