Something like that.
It appears to be some M-16/M4 derivation (though due the year or release and that Snake fires a full-auto burst a couple of times, I'd say a CAR15 or M16A3), as well as using 10-rd magazine.
Im not a gun expert; This is based on examining the movie (DVD and theatrically) as well as the gun that accompanies the McFarlane toy.
On a side note, does any onehave any idea what equpiment (or good pix of it) of the USPF soldiers, especially EFNY version?
