Got some conflicting information on 223/556 ammo in my AR15. I have a very early 1966 Colt SP1 100% original marked 223 Caliber. I presumed I cannot shoot 556 ammo in my rifle based on recent articles stating I could blow it up. A guy @ my gun club told me that is not an issue with the early SP1's, he said the SP1 barrels are the same barrels that are on the Military M16's and can shoot both without any issues. Any guidance from NES would certainly be appreciated. The last thing I want to do is destroy a 53 year old rifle. This gun is in mint condition I want to try and keep it that way.