Originally Posted by oneyeopn

All S&W M&P15's will shoot 5.56 and .223. I didnt know that some were just labeled .223. all of them I have seen are labeled 5.56 and some are labeled 5.56/223 but if you have one that only says .223 I would ask. Did you purchase the rifle new? There have been threads in the past that have asked this question. But all Smith and Wesson M&P15's are chambered for 5.56.

If yours is labeled .223 then you dont have a S&W Barrel, and I am back to the question. Did you purchase it new?