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