It is a M4, not a A1 variant which is automatic, M4s are used by regular troups, though.
The sound has been inspired from Chammy's sound pack, which are one the most realistic SFX carried out so far for OFP.
This can not be done with Operation Flashpoint because of its engine limits, but it would probably be possible with ArmA.
regards,
Thunderbird
Oh in the editor it says "M4a1" in all of them and not "M4" for me.