Tried running some 5.56 through my AR (16" 5.56 chambered 1:9 twist barrel, carbine gas system) this weekend for the first time, because that's all I could find at academy. I usually reload/buy .223 and have never had any jams after several thousand rounds. I had two 20rd PMAGs, one with Federal XM193 brown box, the other with Independence M193. I was stupid and didn't label them. The first magazine, I had 3 weird stovepipes where the stovepiped brass was stuck on top of a fresh round that was partially chambered (not sure if this is a normal stovepipe, like I said, I've never experienced any jams in an AR). Also, the ammo seemed dirty. The second magazine ran flawlessly. I'm inclined to say the first magazine was the Independence, as I've never had any issues with Federal ammo, but there's no way to be sure. What do you guys think? If nothing else, this has taught me I really need to practice some jam clearing drills, lol.