Typical firearms propel a bullet or other type of projectile through the expansion of gas within a firearm barrel.  The majority of the gas may be expelled out of the front of the firearm barrel together with the bullet.  In certain types of firearms, such as automatic or semiautomatic firearms, a portion of the gas may be used to cycle the action of the firearm, thereby ejecting the used casing and reloading another round of ammunition into the firing chamber. 
Additionally, firearms may be fitted with one or more firearm accessories such as a silencer or noise suppression device.  The noise suppression device may operate to restrict, reduce or otherwise impeded the flow of the gas out the front of the barrel.  Still other firearms may be designed and/or modified to have a shortened barrel.  A firearm with a shortened barrel may also tend to be associated with an increased gas pressure. 
An eye or another portion of the face of a user may be positioned behind the firearm substantially along the line of sight of the barrel.  A portion of the gas which expands within the firearm but does not get exhausted out the front of the barrel may be blown back into the user's face. 
Known firearm gas diversion systems such as U.S. Pat.  No.  6,311,603, U.S. Pat.  No.  8,261,649 and U.S. 2013/0092014 propose integrating a gas diversion feature near the rear portion of a charging handle, however a significant portion of the gas may nevertheless be expelled to the rear of the firearm and/or back into the user's face in these designs. 
This application addresses these and other problems.