The use of automatic and semi-automatic rifles is commonly known to be prevalent in the military.  Such weapons typically employ an upper receiver and bolt action operating system.  One standard weapon for the U.S. Military is the M-16 rifle.  Semi-automatic rifles such as the AR15 type are used in the civilian sector.  Such rifles can be further adapted for single shot action.  The structure and mechanisms of semi-automatic and automatic rifles have been the subject of much refinement and variation over the years. 
While there have been advances in the designs of prior art rifles, there remains room for additional improvements.  The present invention is directed toward providing various improvements to semi-automatic and automatic rifles.