Took my SU-16 out yesterday to get the scope sighted in and do some plinking. That went pretty good and I was getting some decent groups when I was taking my time. Shot about 100 rounds of American Eagle .223 in various mags without any problems. I've had a 300 round sealed bag of 5.56 laying around so I decided to try it out. I loaded up a factory 10 rounder and settled in. First shot went well, but didn't eject. It was stuck in the chamber. It tried to feed the second round and jammed. I removed the second round. The bullet was pressed into the casing pretty good. I used a cleaning rod to remove the stuck casing. I examined it and noticed that the rim was chewed up where the extractor tried to remove it. I thought "this isn't good" so I reinserted the mag and fired again. Everything functioned fine. I slowed fired the remaining shells with no problems. I hope to try it some more soon and see how the surplus stuff does.