I was reading about the bushmaster/magpul ACR, and i got a link to a youtube video (sorry i dont have it now) and it says somthing about a gas shut off valve or somthing along those lines.. what exactly does the gas shut off do? The only thing i can think of is that it stops the automatic cycling of the bolt after each round is fired and converts the rifle to manualy operated, like cocking the weapon after each shot?.. this is my guess.. possibly for special operations where as the weapon cycling makes to much noise when a sound surpresser is attached? 
please can some one help me out here.
-Dean
please can some one help me out here.
-Dean




















































