It just seems wrong to switch between 5.56 and .223...maybe it's blind ignorance, but I can't get myself to switch back and forth. I've been putting 62 grain 5.56 rounds through my M&P15T on the range. After I dropped in the Geissele trigger, even with the cheap ammo I get a decent grouping. I just ordered some 75 grain Hornady Match rounds to see if I can tighten the grouping even more. But for run-of-the-mill plinking, I think I'll stick with the 62 grain M855s from Lake City or IMI...fairly inexpensive...not $279 for 1000 rounds inexpensive, but enough to fit in my budget.