I've searched on here but haven't found the answers to a couple of questions I have. I bought a bushmaster XM15-E2S a couple of years ago. Haven't done any performance upgrades really, more cosmetic then anything. So far I've got four rail forearm, 3-point sling, forearm grip, and a surefire mount. Can anyone recomend a good gas block with at least a top rail for a back up iron sight? The only problem I've had is it's jammed several times. Out of the 400-500 rounds I've fired through it I'd say it's jammed 25-35 times. It's always the exact same malfunction as far as I can tell, the empty case that is being ejected gets jammed in the ejection port when the bolt slides forward after the shot. I've tryed about 14 different magazines and haven't noticed any magazine that jams more then the others. It's always thoroughly cleaned after I shoot so I don't imagine that is the problem. I've only tryed one type of ammo (XM855PD) because I bought 1000 rds. It seems that it mainly jams after several full magazines have been shot through it. Anyone have any ideas? Oh yeah, it's the 14.5 Brl with the 1.5 izzy suppressor and collapsible stock if that helps.