To fellow BOGs: If you plan to change the barrel of your AR/M16, please be aware that .223 cal and 5.56mm chambers are very different from the two. I found this out when reading the FAQ at Bushmaster(www.bushmaster.com). I recall a friend of mine in the Philippines who was very excited to show me his M16 that he changed with a stainless target barrel. Little did he know that the barrel was chambered for the 223 caliber. 5.56 cal chambers have a longer leade compared to the 223 cal. chambers. As we know the Philippines, 5.56mm rounds are very common, but not 223 cal. The difference may not be detected visually, but long term use of 5.56mm bullets in .223 cal chambers might create a KB due to increase in pressure caused by copper build-up in the chamber. It may not happen to a new barrel, but when the chamber gets a fair amount of copper build up, then things can go wrong. The FAQ at Bushmaster also states that you could use 223 cal. bullets in 5.56mm chambers but not the opposite. Just a heads up.