The latest issue of American Rifleman has an article comparing NATO 5.56 and .223. It says that while it's fine to shoot .223 in the NATO chamber, low pressure .223 ammo might not cycle properly. What constitutes low pressure?
Although I haven't gotten my XCR yet, I have purchased .223 ammo from various companies already because of rising ammo prices. I have bought Winchester Super X, Remington UMC, and American Eagle; bullets range from about 50gr-65gr, in FMJ, SPS, and JHP. Do you think I'll have any problems with any of these?