The rifle operates by features that are incoporated into the m4 but uses ak47 mags.This rifle was created so that American Special forces in Afganistan can use the captured ak47 magazines instead of leaving them sparly and wasting it.A silencer was also manufactured for that particular rifle and a picctany rail was constructed so that red dot scopes/acog scopes/reflex scopes can be fitted as well.
Picture and much more detailed explaination:
http://quarterbore.com/kac/sr47.html