I have an Olympic Arms upper (11.5 inch)obtained in the mid 90s and I was wondering if this has the military or the civilian chamber dimensions. I have shot both military and civilian brands of ammo through it with no issues at all but with all this talk of the differences between both and possible consequences of shooting military ammo through a civilian chamber I am now curious as to what the dimensions actually are. There are no markings on the barrel or receiver to indicate any specific caliber. I believe the twist may be 1 in 9.
Also, would the Armalite 14.5 inch uppers be civilian chamber dimensions or are they military??
