My father past away a short time ago and now we are starting to go through some of his gear. I came across a few uppers for his AR and i cant identify this one barrel. My mother thinks it was just for shooting 22lr for his .22 conversion b/c the muzzle hole it notably smaller then the 5.56 barrels, but im not sure. It is 24 inches and i tried to measure the muzzle but i cant get and accurate measurement its coming up at 5.54 to 5.55. I took it to the local gun shop and they could not give me any answers. There are no markings on the barrel what so ever. here are a few pics i just took with my camera phone. Any help would be great thank you in advance.