Just curious...do you have a preference between 5.56 NATO rounds vs. .223 Remington rounds in your AR-15? Since I bought my M&P15T, I've only used 5.56 NATO rounds. I don't really have a good reason as to why. Are there any noticeable difference in performance between the 5.56 and .223? Will the .223 allow the rifle to have a longer life since it fires with less pressure?